The Science of the Ocean : The Secrets of the Sea Revealed 9780241415252

Table of contents :
contents
marine world
what are oceans?
ocean history
ocean climates
ocean depths
rocky coasts
surviving in the splash zone
anchoring to the seabed
coastal erosion
growing above the tides
surviving low tide
from coast to coast
rasping rocks
clinging on
combing for plankton
lodging in a shell
waves
fish on land
fish shapes
rock pool territory
cold-blooded diving
seas of colour
cliff nesting
northern gannet
hopping on rocks
sandy beaches
growing in wind-blown sand
lifelike seas
nesting on beaches
beaches and dunes
drama on the seas
american crocodile
beachcombing
tsunamis
estuaries and mudflats
living in sediment
tides
seabed stinger
concealed danger
sensing electricity
migrating to breed
mud probing
the dutch golden age
sweeping for food
fishing with feet
mangroves and salt marshes
growing in salt marshes
colonizing roots
growing on stilts
living upside-down
living fossil
salt water
waving crabs
hunting above water
impressions of the sea
adapting to changing salinity
coral reefs
simple bodies
making rock
synchronizing spawn
horny skeleton
living in a colony
corals
powered by sunlight
stinging for prey
coral reefs
blooming with poison
fanning the water
giant clams
collecting weaponry
changing colour
art meets science
cleaning hosts
making a mask
seabed feeding
blue under water
inflatable bodies
aboriginal sea stories
mutual protection
sex changer
reef feeders
bladed fish
reef fish
cryptic fish
specialized fins
seas of antiquity
reef scrapers
coastal seas
absorbing light
giant kelp
underwater meadows
producing light
alternating generations
asia’s sea deities
living in a tube
stinging bristles
flapping to swim
changing buoyancy
hurricanes and typhoons
jet propulsion
nudibranchs
heavy bodies
suspension feeding
the great wave
walking with arms
tube feet
starfish
spiny skin
scalloped hammerhead shark
flying under water
swim bladders
keeping out of sight
sea-level change
all-over senses
migrating in schools
great frigatebird
plunge diving
sea otter
grazing on grass
humpback whale
upwelling and downwelling
atlantic spotted dolphin
open oceans
dividing labour
phytoplankton
staying afloat
sustaining life in the dark
new ocean floor
deepwater giants
branching arms
jellyfish and hydrozoans
filter-feeding sharks
ocean currents
white shark
slow giant
mapping the seas
lights in the dark
built for speed
wandering albatross
bulk feeding
destruction of the oceans
orca
polar oceans
sea butterfly
sea-ice
polar swarms
antifreeze in fish
zooplankton
king penguin
insulating layers
southern elephant seal
sensitive whiskers
ice-shelves and icebergs
multipurpose fur
narwhal
glossary
index
acknowledgments

Citation preview

The S C I E N C E of the

OC E AN

First published in Great Britain in 2020 by Dorling Kindersley Limited DK, One Embassy Gardens, 8 Viaduct Gardens, London SW11 7BW

DK LONDON Senior Editor Peter Frances Editors Polly Boyd, Jemima Dunne, Cathy Meeus, Annie Moss, Steve Setford, Kate Taylor Managing Editor Angeles Gavira Guerrero Production Editor Kavita Varma Production Controller Meskerem Berhane Associate Publishing Director Liz Wheeler Publishing Director Jonathan Metcalf

Senior Art Editor Duncan Turner Designers Francis Wong, Simon Murrell Photographer Gary Ombler Illustrator Phil Gamble Senior Jacket Designer Akiko Kato Jacket Design Development Manager Sophia MTT Managing Art Editor Michael Duffy Art Director Karen Self Design Director Phil Ormerod

Copyright © 2020 Dorling Kindersley Limited A Penguin Random House Company 10 9 8 7 6 5 4 3 2 1 001–316839–Oct/2020 All rights reserved. No part of this publication may be reproduced, stored in or introduced into a retrieval system, or transmitted, in any form, or by any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission of the copyright owner. A CIP catalogue record for this book is available from the British Library. ISBN: 978-0-2414-1525-2 Printed and bound in China

FOR THE CURIOUS www.dk.com

Contributors

Consultant

Jamie Ambrose is an author, editor, and Fulbright scholar with a special interest in natural history. Her books include DK’s Wildlife of the World and The Science of Animals.

Marine ecologist, author, and television presenter Maya Plass is Head of Communications at the Marine Biological Association, UK, and an honorary fellow of the British Naturalists’ Association.

Dr Amy-Jane Beer is a biologist and naturalist. She began her career studying sea urchin development at the University of London before becoming a freelance science and nature writer and an advocate for wildlife and the natural world. Derek Harvey is a naturalist with a particular interest in evolutionary biology, who studied Zoology at the University of Liverpool. His books include DK’s Science: The Definitive Visual Guide, The Natural History Book, and The Science of Animals. Dr Francis Dipper is a marine biologist and author and has been studying marine wildlife on the seashore and underwater, worldwide, for over 40 years. She has written numerous books for both children and adults. Her Guide to the Oceans won the Royal Society Aventis Prize for Junior Science Books in 2003. Esther Ripley is a former managing editor who writes on a range of cultural subjects, including art and literature. Dorrik Stow has a long career of research and publication on the oceans. He is Professor of Geoscience at the Institute of Geo-Energy Engineering Heriot-Watt University, UK, and Distinguished Professor at the China University of Geoscience, Wuhan, China.

The Natural History Museum, London, looks after a world-class collection of over 80 million specimens spanning 4.6 billion years, from the formation of the Solar System to the present day. It is also a leading scientific research institution, with ground-breaking projects in more than 68 countries. Over 300 scientists work at the Museum, researching the valuable collections to better understand life on Earth. Every year more than five million visitors, of all ages and levels of interest, are welcomed through the Museum’s doors.

Half-title page Pale octopus (Octopus pallidus) Title page Giant devil rays (Mobula mobular) Above School of barracuda (Sphyraena) in the Red Sea Contents page Flower hat jellyfish (Olindias formosus)

contents

marine world

rocky coasts

sandy beaches

12

what are oceans?

22

surviving in the splash zone

62

growing in wind-blown sand

14

ocean history

24

anchoring to the seabed

64

lifelike seas

16

ocean climates

26

coastal erosion

66

nesting on beaches

18

ocean depths

28

growing above the tides

68

beaches and dunes

30

surviving low tide

70

drama on the seas

32

from coast to coast

72

american crocodile

34

rasping rocks

74

beachcombing

36

clinging on

76

tsunamis

38

combing for plankton

40

lodging in a shell

42

waves

44

fish on land

46

fish shapes

48

rock pool territory

50

cold-blooded diving

52

seas of colour

54

cliff nesting

56

northern gannet

58

hopping on rocks

estuaries and mudflats

coral reefs

coastal seas

open oceans

80

living in sediment

124 simple bodies

186 absorbing light

256 dividing labour

82

tides

126 making rock

188 giant kelp

258 phytoplankton

84

seabed stinger

128 synchronizing spawn

190 underwater meadows

260 staying afloat

86

concealed danger

130 horny skeleton

192 producing light

262 sustaining life in the dark

88

sensing electricity

132 living in a colony

194 alternating generations

264 new ocean floor

90

migrating to breed

134 corals

196 asia’s sea deities

266 deepwater giants

92

mud probing

136 powered by sunlight

198 living in a tube

268 branching arms

94

the dutch golden age

138 stinging for prey

200 stinging bristles

270 jellyfish and hydrozoans

96

sweeping for food

140 coral reefs

202 flapping to swim

272 filter-feeding sharks

98

fishing with feet

142 blooming with poison

204 changing buoyancy

274 ocean currents

144 fanning the water

206 hurricanes and typhoons

276 white shark

146 giant clams

208 jet propulsion

278 slow giant

148 collecting weaponry

210 nudibranchs

280 mapping the seas

150 changing colour

212 heavy bodies

282 lights in the dark

152 art meets science

214 suspension feeding

284 built for speed

102 growing in salt marshes

154 cleaning hosts

216 the great wave

286 wandering albatross

104 colonizing roots

156 making a mask

218 walking with arms

288 bulk feeding

106 growing on stilts

158 seabed feeding

220 tube feet

290 destruction of the oceans

108 living upside-down

160 blue under water

222 starfish

292 orca

110 living fossil

162 inflatable bodies

224 spiny skin

112 salt water

164 aboriginal sea stories

226 scalloped hammerhead shark

114 waving crabs

166 mutual protection

228 flying under water

116 hunting above water

168 sex changer

230 swim bladders

118 impressions of the sea

170 reef feeders

232 keeping out of sight

296 sea butterfly

120 adapting to changing salinity

172 bladed fish

234 sea-level change

298 sea-ice

174 reef fish

236 all-over senses

300 polar swarms

176 cryptic fish

238 migrating in schools

302 antifreeze in fish

178 specialized fins

240 great frigatebird

304 zooplankton

180 seas of antiquity

242 plunge diving

306 king penguin

182 reef scrapers

244 sea otter

308 insulating layers

246 grazing on grass

310 southern elephant seal

248 humpback whale

312 sensitive whiskers

250 upwelling and downwelling

314 ice-shelves and icebergs

252 atlantic spotted dolphin

316 multipurpose fur

mangroves and salt marshes

polar oceans

318 narwhal

320

glossary

326

index

334

acknowledgments

foreword We manifest an intrinsic fascination with those things on the brink of our knowledge. There’s a romance, a yearning, seemingly a need to wonder about things beyond our reach. Deep space, other planets, aliens … but, as is often cited, we may actually know more about these phenomena than about the inhabitants of our own oceans because 80 per cent of them are unmapped, unobserved, and unexplored for the so very simple reason that this environment is beyond your reach and mine. We are terrestrial, airbreathing mammals, and while some humans swim well, free dive, or use increasingly sophisticated scuba kit or robots to explore the oceanic unknown, the rest of us “land lubbers” just watch the waves. Beneath those waves is another world, one that, thanks to science and technology, we are learning a lot more about, a lot more quickly. And, as this fabulous book shows, it is almost incomprehensibly beautiful and fantastic. From the smallest to the largest, the shallows to the deep, the fierce to the fearful, these organisms share our planet but live in a different dimension. How exciting! So here is an opportunity to meet the neighbours, the “wet ones,” the extraordinary diversity of miraculous life that has evolved in the oceans. And yet, remote as it can seem, the cultural aspects of our relationship with the sea reveal how we have always had a close connection to this charismatic, dangerous, and rewarding realm. But the tides have turned. Now we are the greater danger, and no drop of our seas is secure. Coral reefs are bleached. Plastic litters the greatest depths and fills the bellies of turtles and whales and chokes albatross chicks. The acidification of the water, pollution, and overfishing threaten the entire ocean ecosystem. There has never been a more important time to immerse ourselves in the wonder of the briny world and thus learn to love and protect it. Dive in, swim among stranger things, and then stand up for our oceans.

CHRIS PACKHAM NATURALIST, BROADCASTER, AUTHOR, AND PHOTOGRAPHER

SILKY, DUSKY, BLACK-TIP, AND GALAPAGOS SHARKS FEED WITH YELLOWFIN TUNA AND RAINBOW RUNNERS ON A SHOAL OF SCAD

marine world

the

Almost as old as Earth itself, oceans dominate the planet’s surface. Life first evolved in the oceans, and today they are home to a vast diversity of species. By transporting huge amounts of energy, the oceans also help to power and modify Earth’s climates.

what are oceans? Earth is a watery world, with 68 per cent of the surface covered by saltwater oceans. Each of the five major ocean

The second largest ocean basin, the Atlantic spans around 20 per cent of Earth’s surface

basins (the Arctic, Atlantic, Indian, Pacific, and Southern) is a deep depression in Earth’s surface. Connected to the oceans, and typically partly enclosed by land, are numerous smaller seas such as the Mediterranean and Bering seas. Oceans are

marine world

12 • 13

partially separated by landmasses but are all interconnected.

Ocean strength The oceans reveal their strength in the waves that crash onto shorelines around the world. Heading towards a shallow reef, this mountainshaped wave off the south coast of New South Wales, Australia, will break as its base touches the seabed and frictional drag slows it down.

Oceans from space Composite satellite images from space show clearly how oceans predominate over land. This view of Earth’s western hemisphere shows the Atlantic Ocean.

EARTH’S PROPORTIONS Oceans are immense, holding most of the water on Earth and having an average depth of about 3,700 m (12,000 ft) and a total volume of 1.34 billion cubic km (321 million cubic miles). Around 2 per cent of Earth’s water is locked up as snow and ice, leaving 1 per cent as free-moving fresh water. The largest ocean is the Pacific, spanning 153 million square km (59 million square miles) and containing 49 per cent of Earth’s salt water.

KEY Salt water (68%) Land (29%) Fresh water (3%)

Complex, frilly suture lines help with species identification

The ammonite’s head and tentacles once projected from here

Patches of original shell material remain after fossilization

Past life Ammonites were cephalopods common in the oceans of the Jurassic (200–145 MYA) and Cretaceous (145–66 MYA) periods, but they died out around the same time as the dinosaurs. Dead ammonites sank to the seafloor where they were covered in sediment and eventually fossilized in rock. This fossil (Desmoceras latidorsatum) from the mid-Cretaceous period was found in coastal Madagascar.

Coral fossil Evidence that chilly Scotland was once part of a landmass near the equator, comes from warmth-loving fossil corals found there and dating to around 350 million years ago.

14 • 15

The familiar layout of Earth’s continents and oceans is very different from the way it was in the prehistoric past. Today’s oceans and their seas arose gradually as early landmasses split up and moved apart. Scientific evidence suggests that the original ocean formed from water vapour that escaped from the molten surface of the planet. Around 3.8 billion years ago, conditions cooled and this vapour started to condense and fall as rain.

OCEANS OF THE PAST Continents have come together and moved apart several times in Earth’s history. Evidence for this comes from the “ jigsaw” fit of continents such as South America and Africa, as well as palaeontology studies. Continents slowly change their positions through volcanic processes happening deep beneath the oceans. Today the Atlantic Ocean is getting bigger and the Pacific Ocean and Red Sea are getting smaller, but by less than 2 cm (3/4 in) per year.

Cretaceous ocean

Cretaceous continent

LAURASIA

GONDWANA

CRETACEOUS PERIOD C.130 MYA

marine world

ocean history

Stormy seas Oceans, atmosphere, and land all interact to create our climate and weather. Dramatic supercell thunderstorms over land or sea – here above Australia’s Queensland coast – occur when wind conditions cause strong rotating updrafts. The frequency and intensity of extreme weather events is increasingly linked to humaninstigated climate change.

Foraminifera have thin shells called tests

Ocean thermometers

ocean climates The world’s oceans and their climates are inextricably linked through a complex web of interactions. The oceans absorb and store heat from the Sun, especially at the equator. From here, wind-driven surface ocean currents circulate water around each of the main ocean basins. In turn, the Sun’s heat and Earth’s rotation set the pattern of prevailing winds. Rainfall is highest in tropical areas, because the oceans are warmest here and so evaporation is high. The oceans slowly release heat, which is why the oceanic climate found around continental coastlines is less extreme than the climate far inland.

CLIMATIC DISTURBANCES Increased carbon dioxide in the atmosphere traps heat and causes ocean temperatures to rise as it absorbs extra heat. This can also lead to more extreme instances of the climatic disturbances known as El Niño and La Niña. The El Niño effect occurs where winds and currents in the equatorial Pacific are disrupted, leading to above-average sea-surface temperatures. The ONI records the difference between recent averages and the 30-year average temperature.

Oceanic Niño Index (ONI) ºC

marine world

16 • 17

Analysing the chemical composition of sandgrain-sized fossil shells of microorganisms called foraminifera can help determine past sea-surface temperatures. Living foraminifera such as Rosalina globularis, above, are still found throughout the oceans.

2008

Values above 0.5 indicate warmer El Niño events

Values below -0.5 indicate cooler La Niña events

2010

2012

2014 Year

2016

2018

3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 2020

ocean depths Marine organisms inhabit a vast, three-dimensional space and can be found from the water surface down to the deepest depths. An organism near the surface will experience very different conditions to one in the deep ocean. Scientists divide the oceans into zones of decreasing sunlight and temperature, but pressure increases

DEPTH ZONES Marine life has adapted to the different ocean depths. Phytoplankton, the basis of almost all ocean food webs, only grow in the sunlit zone. In the twilight zone where light is limited, animals swim upwards at night to feed on plankton and then down for safety in the day. In the dark midnight zone animals produce bioluminescent light to hunt or communicate, while abyssal animals gather dead material or particles that drift down from above. Deep ocean trenches form the dark hadal zone.

continuously from the surface to the deep. Surface layers are well-lit and have a good supply of nutrients and food. In deep zones, the

PHYTOPLANKTON

sunlight fades and temperatures decrease, which limits life there. MACKEREL

SUNLIT ZONE 0–200 m (0–650 ft)

Deep ocean and sandy shallows In the Bahamas, the Berry Islands form a semicircle enclosing sheltered, sandy plateaus. This satellite image shows depth contours beneath the clear water. Deep ocean borders the land at the top, while Chub Cay at the bottom drops into the tongue of an ocean canyon.

SQUID

TWILIGHT ZONE 200–1,000 m (650–3,300 ft)

18 • 19

ANGLERFISH HATCHETFISH

GRENADIER FISH

Feeding tentacles catch drifting plankton and organic particles

GIANT AMPHIPOD

ABYSSAL AND HADAL ZONES 4,000–11,000 m (13,000–36,000 ft)

Cold-water coral Most corals live in shallow waters, but cold-water corals, such as Lophelia pertusa, form reefs in twilight and midnight zones. Without the nutrients provided by surface-level symbiotic algae, these corals grow very slowly.

marine world

MIDNIGHT ZONE 1,000–4,000 m (3,300–13,000ft)

rocky coasts A rocky coast provides a solid, dependable foundation for many plants and animals. Although there is often a risk of being swept away, a tidal pool or a high-rise cliff can also provide a refuge.

The branching straps of Ramalina form scattered clumps on the rocks

Tufted lichen

22 • 23

Grey Ramalina siliquosa and some other lichens grow as upright tufts. Ramalina usually lives at a higher level than yellow Xanthoria (see right) on European shores.

Maritime lichen The sunburst lichen (Xanthoria parietina) of northwest Europe is typically found inland, but it can also tolerate the salty habitat of rocky shorelines. Its flat orange body, or thallus, may occasionally even be covered by the highest spring tides.

surviving in the splash zone

rocky coasts

Little life can thrive on wave-splashed rocks, which are too far from the reach of the tide for underwater organisms to survive and too hard for plants to root. But lichens have the resilience to grow here. In fact, they are so successful that in places they grow in prominent, colourful patches along the coastline. Key to their success is an intimate partnership: each kind of lichen consists of a nutrient-absorbing fungus that clings firmly to the rock and a pigmented alga that photosynthesizes to make food.

INTIMATE PARTNERSHIP The bulk of a lichen consists of the filaments of a fungus. Called hyphae, these filaments attach to the hard substrate and, as in other fungi, provide a large surface area for absorbing nutrients from organic food such as detritus and bird droppings. But more than 50 per cent of the lichen’s food is made from atmospheric carbon dioxide by its photosynthetic algae, which share the food they produce with the fungus.

Algae and hyphae filaments disperse on wind to establish new lichen colonies Algal cells Fungal hyphae

Rootlike hyphae called rhizines attach the lichen to the rock

SECTION THROUGH A LEAFY LICHEN

24 • 25 rocky coasts

The photosynthetic frond produces sugars, including mannitol, which is often exuded as a sweet powder on the frond’s surface, thus inspiring this species’ name

Giant seaweed Sugar kelp (Saccharina latissima) of the northeast Atlantic grows particularly well when sheltered from extreme waves. Here, on the lower shore, its fronds can reach 4 m (13 ft) in length, which helps them extend further upwards to catch sunlight when lifted by the high tide.

The stipe, or stem, keeps the frond raised towards the light at high tide for photosynthesis

In the core of the stipe, filaments of conduction cells help to transport sugars around the kelp; seaweeds lack the transport vessels of true plants

The holdfast, unlike the roots of true plants, does not take up any nutrients, leaving the frond to absorb most of the material needed for photosynthesis

A crinkly edge to the frond is a characteristic of the sugar kelp

Brittle stars cling to the holdfast with their sinuous arms

Holdfast communities Branching holdfasts can provide a microhabitat for diverse marine invertebrates. Among the holdfasts of kelp growing on California’s Pacific coast live scavenging brittle stars and purple urchins that graze on the seaweed.

Purple urchins are the dominant grazers of California kelp

anchoring to the seabed Hard, rocky coastlines are impossible habitats for true plants to send down roots, but here – between the tides – conditions are perfect for the leafy algae popularly known as seaweeds. Instead of roots that penetrate, seaweeds have structures called holdfasts that cling to the substrate. Some holdfasts are like suckers, but others grow dense thickets of tendrils that anchor the seaweed to the seabed and shelter tiny invertebrates, while the alga’s long, trailing fronds absorb light for photosynthesis.

HOLDFASTS A young seaweed develops into a frond, stipe (stem), and holdfast. The holdfast consists of branching, fingerlike projections called haptera, which envelop rocks and stones and become bushier in deeper water. It secretes mucopolysaccharide – a natural adhesive – as it grows larger, to support a bigger frond. Thick, bushy growth More branches to holdfast

Growth is mostly horizontal

SHALLOWS

MID-DEPTHS

DEEP WATER

Worn away by waves Over millennia the forceful churning action of waves crashing against this coastline on the Hawaiian island of O’ahu has unevenly worn away the rock to create a network of inlets and promontories.

coastal erosion The coastlines of every continent undergo constant change. In some areas the land area expands, but in others the coastline is worn away by erosion. Coastal erosion is determined by three main interacting factors: marine energy (waves, storms, and tides); the relative hardness of the rock; and tectonic activity (earthquakes and uplift). The rate of coastal retreat can be more than 100 m (330 ft) per century in areas where severe storms pound a soft sand-and-clay shoreline. Hard granite cliffs may chemical attack, wave impact, and relentless abrasion by sand and gravel all help to break down rocks and boulders along the shore.

HEADLANDS, ARCHES, AND SEA STACKS Soft rock on a coastline is worn back by wave action into bays, while harder rocks provide more resistance and form headlands, which are subject on three sides to focused wave action. Eventually this creates notches and sea caves at the waterline. The caves enlarge from either side of a headland, and the sea eventually breaks through to form arches, which later collapse, leaving isolated sea stacks. Bay formed in area of eroded soft rock

Sea cave

Hard rock resists erosion to form headland Arch

Wave energy focused on headland

Sea stacks formed from collapsed arch

rocky coasts

Storms, tidal currents, and rip-currents carry the sediment out to sea.

26 • 27

remain stable for hundreds of years. Landslides, rockfalls,

TAP ROOTS Sea thrift has a woody tap root that can reach more than 1.5 m (5 ft) into coastal sediment, often winding between rocks or plunging into cliff faces. The tap root typically grows vertically downwards and helps to anchor the plant firmly onto a shoreline that may be buffeted by strong winds.

Adventitious (branching) roots are more dense and spreading in shifting sand

The tap root grows thick, keeping the plant firmly in place

rocky coasts

28 • 29

ROOT SYSTEM

growing above the tides On the very edge of the ocean world, beyond the reach of normal tides, is a community of coastal species that belong to the land but live exposed to the sea’s spray. Salt and wind are dehydrating: salt landing on foliage draws water from tissues by osmosis, while wind increases evaporation. The flowering plants that survive here must be adapted to resist these effects. Some, such as sea thrift, have thin, straplike leaves with a small surface area that reduces evaporation and a thick cuticle that traps water inside.

A butterfly feeding on nectar helps to crosspollinate sea thrift; even the pollen of this plant is salt-tolerant

Coastal pollinator There are few marine insects, but some land species, such as this black-veined white butterfly (Aporia crataegi), are drawn to the nectar of coastal blooms, such as sea thrift. Other insects feed along the strandline of the beach.

Tough plant Sea thrift (Armeria maritima) thrives on windswept coasts around the northern hemisphere. By hugging close to the ground, its leaves are able to resist the elements, while its salt-tolerant tissues help the plant to grow in soil that may get occasionally inundated by extreme tides.

Retracted tentacles reduce the animal’s surface area, so there is less evaporation when it is uncovered by the retreating sea

Dealing with exposure By pulling its tentacles into its body column, a beadlet anemone not only avoids predators but also retains more water while exposed to the air at low tide.

Body column contains muscle fibres that contract to pull the tentacles inside

surviving low tide The intertidal zone is the place where the ocean meets the land, but the

30 • 31

living things that make it their permanent home come from the sea. Most of these organisms need to be underwater to breathe, feed, and reproduce. At low tide, those that can walk, such as crabs, can follow the water or shelter under rocks. Others that are fixed to the spot, including anemones,

rocky coasts

have no option but to wait for the waters to return.

Tidal pool A pool on a rocky shore left by the ebbing tide is a safe haven for beadlet anemones (Actinia equina). Here, ocean animals can stay active, even when the surrounding rocks are left high and dry.

INTERTIDAL ADAPTATIONS These shore anemones illustrated in Ernst Haeckel’s Kunstformen der Natur (1904) have variable intertidal adaptations. The daisy anemone (Cereus pedunculatus; top middle) lives partly buried and retracts completely when disturbed or exposed. Less-retractile species rely on a sheltered location to survive: the jewel anemone (Corynactis viridis; bottom left), drawn here with drooping tentacles, prefers rocky caves, while the plumose anemone (Metridium senile; bottom right), with feather-like tentacles, hangs limp from rocky overhangs at low tide. Such vulnerable species are more abundant where they are permanently submerged.

HAECKEL’S SEASHORE ANEMONES

West Point, Prouts Neck (1905) US artist Winslow Homer painted his favourite watercolour just after sunset, capturing a column of seaspray leaping above the rocks. It followed several days of intense observation of the light and tides across Saco Bay, close to the artist’s studio in Maine. The vivid reds and pinks, drenching the sky and sea, and the bold composition show leanings towards Expressionism.

The Life Boat (1881) In the 1880s, Winslow Homer’s art focused mainly on the struggle of fishing communities against the sea. This atmospheric pencil and wash study, which was the basis for a larger watercolour, depicts men in oilskins forging towards a ship in danger.

the ocean in art

from coast to coast In the second half of the 19th century, the US was a young country in Artists sought to introduce audiences in the eastern states to the aweinspiring mountains, plains, and seascapes to the west. The patriotic spirit

32 • 33

search of an art culture that would reflect back the glory of a new nation.

captured in their work was reinforced by songs such as America the

While Impressionist artists in Europe were rebelling against classical art forms, these were still preferred by many contemporaries in the US. The sublime landscapes of English-born American artist Thomas Cole, founder of the Hudson River School, an art movement that flourished in the mid-19th century, drew on Romanticism as well as realist and naturalist styles. The German-American painter Albert Bierstadt’s grandiose peaks and plains, sketched during an expedition in the American West, were romantic constructs that sold idealized notions of the American Frontier to new settlers. He

When you paint, try to put down exactly what you see. Whatever else you have to offer will come out anyway. WINSLOW HOMER, TO ARTIST FRIEND WALLACE GILCHRIST, c.1900

also travelled to the West Coast, where he painted rugged rocks and crashing waves. Meanwhile, in the east, Fitz Henry Lane painted the coastlines of Maine and Massachusetts in Luminist style – a form of realist landscape painting characterized by precise brushwork and ethereal light. Arguably, the pre-eminent American marine artist in the 19th century was Winslow Homer, known mainly for his oil paintings and watercolours. His early works depicted scenes of contemporary life in the US, but his art gained new depth after he spent 18 months on the British Tyne and Wear coast, where he painted the daily lives and hardships of local fishermen and women. He later retreated to a remote cottage and studio in Prouts Neck, on the East Coast in Maine, where he created magnificent seascapes that captured the energy and raw beauty of the ocean. Although he travelled and painted the iridescent seas off Bermuda and Florida, he always returned to Prouts Neck, where the ocean continued to provide a source of inspiration until his death in 1910.

rocky coasts

Beautiful, which celebrated a land that stretched “from sea to shining sea”.

Visible scratches are left because the limpet’s radula is harder than the surface rock

THE MOLLUSCAN RADULA A snail’s “tongue” – correctly termed an odontophore – moves in and out of the mouth. In doing so, it rubs the radula over the substrate. The radula is covered with tiny teeth made from hard chitin (the same material found in invertebrate exoskeletons). As the teeth get worn down, the radula is regenerated, growing from a sac at the base of the odontophore.

Radula sac

Retractor muscle pulls odontophore into the mouth

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RADULA STRUCTURE

Toothed radula is carried on the odontophore

Protractor muscle projects the odontophore

Abrading limpet To dislodge the toughest algae, the radula of a limpet (Patella vulgata) has teeth reinforced with an iron compound. The material of these teeth is the hardest produced by any animal.

rasping rocks Sea-covered rocks are coated in a film of microorganisms, algae, and organic detritus, providing a source of food for many grazing animals. Dominant among them are molluscs, including a huge variety of herbivorous snails and limpets that rasp the surface as they crawl from place to place. Key to their success is their grazing equipment: a muscular “tongue” that scrapes the rocks with an abrasive ribbon called a radula, dislodging the nutritious material, which is then swallowed.

Groove in foot releases sticky slime from abundant mucus-secreting cells, helping the topshell to cling onto rocks

Body retracts into shell when danger threatens; a horny “door” called an operculum then seals the opening

Muscular foot carries the weight of the topshell as it creeps over rocks

Sweeping snail The painted topshell (Calliostoma zizyphinum) is a subtidal grazer of rock-dwelling microorganisms, found at depths of up to 300 m (1,000 ft). As in most topshell species, its radula works like a fine brush to sweep loosely bound food particles from rocks; unlike that of a limpet, it lacks the resilience to harvest algae that adhere more tightly.

The shell stays looking bright and unworn – perhaps the result of the topshell sweeping its mucus-coated foot over the shell’s surface, which deters algal growth

Spots and bands of purple and crimson pigments, called porphyrins, pattern the shell; the pigments may be derived from the topshell’s diet

Tentacle contains tactile and chemical sensors to help with navigation while grazing on rocks

Small, cup-shaped eye on a short stalk senses light and dark; the eyes help the animal to stay in the shade and avoid being exposed to predators by sunlight when grazing

Attached by a thread California mussels (Mytilus californianus) lack the limpet’s clinging foot. Instead, they tether themselves to rocks with a bundle of protein fibres known as a byssus.

Fibres adhere to rock with a kind of protein glue (a different protein to that forming the fibres)

clinging on Organisms that live on rocky shores exposed to battering waves are constantly at risk of being washed away. Those that lack the agility to dodge tightly. Limpets are well equipped to survive the worst of the ocean’s fury: they have a cone-shaped shell that clamps down firmly, a muscular foot

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the breakers and find shelter in crevices must do what limpets do – cling on

that works like a suction cup, and sticky mucus that acts like glue.

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Intertidal life Common limpets (Patella vulgata) of northwest Europe – seen here sharing their rocky habitat with smaller periwinkles and barnacles – hold fast at low tide during the day. They emerge from their shells only when submerged, or at night, to graze on algae.

WAVES AND SHELL SHAPE A limpet clamps down by contracting muscles that pull the shell towards the rock, reducing pressure under the foot so that it functions as a sucker. The foot also secretes sticky mucus that helps to seal the attachment. Where there is little wave action, limpets grow flatter shells. Stronger waves cause the limpet’s muscles to contract more in order to take the extra strain. This affects the shell-secreting tissues, producing a taller and more conical shell shape.

Muscles are less contracted Growth is mainly outwards

Edge of shell pulled loosely onto rock

LITTLE WAVE ACTION Edge of shell pulled tightly onto rock

Growth is mainly upwards Muscles contract more

GREATER WAVE ACTION

combing for plankton Acorn barnacles can be so abundant on a rocky shore that their small, volcano-shaped shells form a distinct white band. Each “volcano” opens at high tide so that the feathery limbs of the crustacean inside can reach up into the water. By quickly waving back and forth in a combing motion – or simply letting the backwash run through their “feathers” – the limbs catch nutritious detritus, algae, and the tiniest animals of the zooplankton.

ZONES ON SHORELINES Barnacles more tolerant of dehydration can live further up the shore, where low tide exposes them for long periods. In Europe, for example, Chthamalus montagui can survive above Semibalanus balanoides, but it cannot thrive lower down due to competition from S. balanoides for space to feed. Similar barnacle zonation occurs around the world.

Smaller Chthamalus montagui predominate on upper shore

HIGH TIDE Larger Semibalanus balanoides predominate on middle shore Predation and competition from other animals prevents barnacles colonizing lower shore

LOW TIDE

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Casting the net Magnified many times, the thoracic limbs, or cirri, of a grey acorn barnacle (Chthamalus fragilis), from eastern North America, are seen to carry long hairs, called setae. The setae overlap to create a trap that catches particles as small as two-thousandths of a millimetre in size.

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A diamond-shaped aperture, here closed at low tide, is characteristic of the northern acorn barnacle (Semibalanus balanoides) of Europe and North America

Exposed and closed Barnacles cannot feed at low tide, so they withdraw their limbs, then close their shells using moveable plates that seal the entrance. Like this, they are protected from desiccation until the tide returns and they become active again.

Octopus extends its arms to push open the clam shell

Suckers grip the shell as the arms pull it closed

Flexible arms coil around the body so the octopus can fit into the shell

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The crab’s borrowed shell is often colonized by other animals; this whelk shell is covered in snail fur (Hydractinia echinata), a kind of colonial hydrozoan

Octopus in a shell Hermit crabs are not the only animals to use shells for protection. Along tropical shores, the coconut octopus (Amphioctopus marginatus) sets up home in a variety of objects, including coconut shells and, as here, the hinged shells of clams.

Two larger pairs of legs are used for walking; two smaller pairs, hidden from view, are used to grip the inside of the shell

lodging in a shell Only the top of a hermit crab’s head is shielded by a hard carapace; the rear half of its body is soft and vulnerable. For this reason, hermit crabs spend their lives lodged for protection inside a coiled snail’s shell. They use their strong limbs to drag this mobile sanctuary with them wherever they go. When a crab grows too big for its shell, it seeks an upgrade – carefully testing the new shell’s size and weight before making the switch.

CRAB ANATOMY COMPARED Most crabs have a short, flaplike abdomen that folds beneath the hard carapace of their body and is all but concealed. But in hermit crabs, the long, soft abdomen twists to one side, which enables it to fit more easily into a coiled snail shell. Tiny, hook-shaped structures called uropods at the abdomen’s tip and small legs along its sides grip the inside of the shell to hold the crab in place.

KEY Carapace Abdomen Walking leg

Claw/pincer Telson Uropod

COMMON CRAB

HERMIT CRAB

Shells for size In their seashore habitat, juvenile European common hermit crabs (Pagurus bernhardus) make use of the most common empty shells found there, including those of periwinkles and dogwhelks. In deeper water, older crabs use the shells of larger snail species.

Long antennae are used as tactile sensors to detect movement

Right chela (pincer) is much larger than the left chela and is more likely to be used in self-defence

Breaking wave This image shows the moment when a wave formed in the open ocean approaches the shore and the rolling “tube” of water collapses to form a breaking wave.

waves A wave is a disturbance in the surface of the sea produced by the transfer of energy from wind to water. Wind-generated waves range in size from a barely ruffled surface and snaking ripples to huge rogue waves reaching a height of up to 10 m (33 ft) that can snap a giant tanker in half. Major storm waves generated in the Southern Ocean around Antarctica can travel for nearly two of Alaska. Their size is diminished, but their distinctive pattern remains the same as when first formed. The amount of energy

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weeks across the Pacific before breaking on the remote shores

stored in waves is enormous – a single storm wave can exert

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up to three tonnes per square metre as it breaks.

WAVE FORMATION The three stages in wave development are known as sea, swell, and surf. The state of random choppiness building to larger irregular waves is known simply as sea. As these waves leave the region in which they were generated, wave interaction slowly develops a distinctive pattern of waves known as swell. Eventually, as a wave train enters shallow water, it interacts with the seafloor. The movement slows, and the distance between the waves reduces, resulting in a relative increase in wave height. Eventually, the ratio of wave height to wavelength reduces to the point where the wave topples forwards and breaks as surf.

Wave forms offshore as swell

Wavelength reduces

Motion of water molecules

Relative wave height increases

Wave breaks

Flexible hunter The small epaulette shark (Hemiscyllium ocellatum) has several adaptations that allow it to hunt in very shallow intertidal pools, where it targets worms, crabs, shrimps, and small fish. The shark is 70–90 cm (28–35 in) long, slender, and flexible, and thus able to manoeuvre easily in small spaces using its sturdy fins. Its flattened underside and blotchy coloration allow it to lie undetected until prey ventures within range.

Short snout, with electroreceptive barbels on the underside, is used to turn over small rocks or burrow in the sand as shark searches for food

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Blotchy upper side provides camouflage against highly textured reef surfaces

Small teeth are suited to grasping and crushing prey

THE WALKING SHARK Epaulette sharks often venture into pools and channels too narrow or shallow for swimming and may find themselves completely stranded by the tide. In these circumstances, they are able to “walk”, or crawl, over rocks or sand, using coordinated movements of the paired pectoral and pelvic fins.

Fins operate in coordinated diagonal pairs

Sturdy, paddle-shaped fins are used for both swimming and “walking” Body flexes

CRAWLING MOTION

fish on land

Eyes can retract into water-filled skin folds to prevent them drying out on land

The intertidal zone is a challenging habitat, with extreme fluctuations in temperature, salinity, and oxygen levels. But it also offers rich feeding opportunities and safety from large marine predators. Fish that live in these waters include the epaulette shark, which can last a few hours out of water, and mudskippers, which can spend up to 18 hours a day on land. To cope with oxygen-depleted waters at low tide, they shut down non-essential metabolic functions, reduce their heart rate and blood pressure, and prioritize the supply of oxygen to the brain.

Prominent shoulder markings (or “epaulettes”) resemble huge eyes and may deter predators

Flattened underside allows the shark to press itself to the seabed without casting a tell-tale shadow and provides stability on land

Fish out of water Found on mudflats, in estuaries, and in swamps, mudskippers (here Periophthalmus barbarus) are the only fish to walk, eat, and court on land. They survive by carrying water in gill chambers.

Flexible spinal column allows movement in tight spaces

Lateral flattening gives quick bursts of speed, sharp turning, and the ability to fit through narrow spaces

Tapering at head and tail permits fast open-water swimming

FUSIFORM Atlantic cod Gadus morhua

COMPRESSIFORM Emperor angelfish Pomacanthus imperator

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Flattened shape enables fish to live on the seabed; it flaps its fins up and down like a bird for swimming

Spherical-bodied fish are slow swimmers that rely on camouflage and adaptations to avoid predators and capture prey on the seabed

DEPRESSIFORM Pacific leopard flounder Bothus leopardinus

Body moves in sinuous waves that pass right through the body; tail (caudal) fin is often more pronounced

ANGUILLIFORM European eel Anguilla anguilla

GLOBIFORM Warty frogfish Antennarius maculatus

Elongated beak and arrowlike body enables fish to swim fast over short distances

SAGITTIFORM Longnose gar Lepisosteus osseus

Ribbon-shape enables fish to hide in rock crevices, but it is a slow swimmer

Thin, threadlike body slithers through water like a snake

FILIFORM Hair-tail blenny Xiphasia setifer

TAENIFORM Crescent gunnel Pholis laeta

Body can be up to 1.5 m (5 ft) long, but weighs only 170–200 g (6–7 oz)

Females and immature males have a birdlike beak that curves outwards and cannot be fully closed

fish shapes The shape of a typical fish reflects the fact that it moves through water – a medium less dense than air – and is affected less by gravity than land animals. A smooth streamlined body, with a rounded cross section and pointed front end, is better for cutting through water, while fins (rather than weight-supporting limbs) control position or help generate thrust. But many fish have departed from this ideal shape to exploit specialized life styles. Dorsal fin runs full length of the body

Extraordinary lengths The pale snipe eel, or deepsea duck (Nemichthys scolopaceus), has around 750 bones in its spine – more than any other animal on Earth. It is found in oceans the world over at depths of 90–1,800 m (300–6,000 ft). Observations suggest that it orientates itself vertically and feeds entirely on mid-water pelagic crustaceans.

Large, sail-like first and second dorsal fins merge to form a continuous, fringelike fin

Throat leads leads to oesophagus, which is particularly rich in blood vessels and may help with breathing in air

rock pool territory A territory is an area of habitat that a single animal, a pair, or a group defends from others of the same species or other species, earning them exclusive access to food, mates, and hiding places. For the shanny (Lipophrys pholis), the advantages of a rock pool territory cut off from others at low tide balance the challenges of life in the intertidal zone (see p.45). Several female shannies may deposit eggs in a pool guarded by one male. At high tide, the male will attack almost any animal venturing near.

Large pectoral fins, with stout bases, provide leverage for moving on land

Shanny on land If stranded by the tide, the shanny hides in crevices or moves over rocks. Its tail sweeps back and forth with enough traction on the ground to help push the fish forwards.

Mottled coloration provides camouflage and becomes much darker in brooding male

TYPES OF FINS All bony fish share a similar arrangement of dorsal, anal, and caudal fins along the midline and paired pelvic and pectoral fins. However, some fins are modified according to the species’ mode of living. For example, the fins of the shanny enable it to swim quickly and strongly against tidal currents and to crawl over land.

Caudal fin provides some propulsion during swimming when swept from side to side

Second dorsal fin

Third dorsal fin

Caudal fin

Anal fin

Pelvic fin

First dorsal fin

Pectoral fin

FINS ON A BONY FISH

Scaleless skin can absorb oxygen from water or air, helping with respiration

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Large eyes provide good vision in both water and air

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Living with limits The shanny’s ability to exchange respiratory gases in air as well as water is a vital adaptation to the oxygen-depleted environment of a rock pool. At low tide, when feeding opportunities are limited, the fish adopts a relatively lowenergy lifestyle, lurking hidden until high tide or until roused to territorial defence.

cold-blooded diving

Blunt face allows front teeth to get close to rock when grazing seaweed

A lizard that relies on the Sun’s rays to stay warm and active is an unlikely cold-water diver – but along the rocky coastlines of the Galápagos Islands in the eastern Pacific Ocean, the marine iguana (Amblyrhynchus cristatus) does just that. On this volcanic archipelago, where competition for land-sourced food is intense, the marine iguana has evolved to eat seaweed. Females and juveniles usually graze between the tides. Large males dive deeper, enduring the chilly Humboldt Current, which comes straight up from Antarctica and streams around these islands.

The skin’s covering of beadlike scales protects the body from physical injury and reduces water loss by evaporation

Dark skin patches absorb the Sun’s radiation well, warming the blood

Specialized teeth The iguana’s jaws are lined with threepronged teeth, which spear the seaweed fronds that the lizard rips from the rock.

SNEEZING SALT

Salty mucus leaves the gland through this duct (tube)

A diet of seaweed quickly loads the body with too much salt, which would disturb the body’s salt/water balance, damaging cells. Sea reptiles and seabirds possess glands that actively pump salt from the blood into salt-secreting glands, from where it leaves the body. The marine iguana, like seabirds, has paired nasal salt glands: the excess salt mixes with mucus and is periodically forced out by sneezing through the nostrils.

Gland where salt is concentrated

Nostril

NASAL SALT GLAND OF MARINE IGUANA

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Conical spines on the head develop in adult, sexually mature iguanas

Cold-blooded diver Like all reptiles, the marine iguana is ectothermic – meaning that it depends upon its surroundings for its warmth. It can last for just over an hour in the cold sea around the Galápagos. Then, before it chills too much to function, the iguana must return to land to bask in the Sun to recharge with solar heat.

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A white crust of salt, expelled from glands in the nostrils, often covers the top of the head

Port-Miou (1907) Georges Braque’s headlong plunge into Fauvism is signalled in his passionate colouring of the high ridges and trees fringing the long inlet of Port-Miou on the coast near Marseille, France. There is a suggestion of Cubism in the diamonds on his cobalt-blue sea.

A Fishing Boat at Sea (1888) The emotional energy captured in the most simple brushwork in Vincent van Gogh’s work was an inspiration to the Fauves.

the ocean in art

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seas of colour When the first Fauve paintings went on show in 1905 at the Salon d’Automne in Paris, France, a critic compared them to the “naive games of a child playing

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with a paint box”. Here were landscapes, seascapes, portraits, and nudes that dispensed with all notions of representation and fidelity to nature. Colour was redefined: flattened shapes of saturated hues were elements of the painting in their own right and vehicles to express the artists’ emotions. The Fauves drew their inspiration from the late 19th-century Post-impressionists, such as Vincent van Gogh, who brought an ecstasy and anguish to colour and brushwork that transformed his subjects. In 1881, Paul Gauguin urged fellow artist Paul Sérusier to use not just green for a tree, or blue for a shadow, but the most beautiful green and the bluest blue. Fauve theories, which would underpin Expressionist, Cubist, and modern art to the present day, emerged while Henri

Matisse and André Derain spent the summer in the fishing port of Collioure, France, in 1905. They experimented with line and colour to capture the enhancing effects of Mediterranean light. Similarly, Georges Braques produced his first Fauvist work in L’Estaque, near Marseille, in 1907. All three artists flooded their canvasses of ports and coasts with bold colours and simplified forms that expressed their subjective response and intensity of feeling rather than objective reality.

We were always intoxicated with colour, with words that speak of colour, and with the sun that makes colours live. ANDRÉ DERAIN, 1880–1954

Rictal rosette is a fleshy flap around the base of the bill’s gape; it gets bigger and turns yellow-orange in breeding birds

The bill’s horny outer sheath – the ramphotheca – grows thicker and more pigmented in breeding puffins, making the bill bigger and more colourful; this helps to reinforce the bond between monogamous pairs

Counter-shaded body plumage – black above and white below – may help to disguise the bird against ocean water when fishing at sea, protecting it from both aerial and underwater predators

Broad bill enables each parent to hold many sand eels – crosswise – at once

EGGS ON LEDGES Eggs are vulnerable in a cliff-face colony. Guillemots – relatives of puffins – lay spotted, pear-shaped eggs on exposed ledges, contrasting with whiter, rounder, typically spot-free puffin eggs hidden in crevices. Distinct spotted patterns may help guillemot parents to recognize their own eggs. The eggs’ less-rounded shape lets them sit flatter and more securely on the nest and spreads the stress of knocks from jostling birds over more of the egg surface, reducing the risk of breakage.

Clifftop chick Like puffins, the closely related razorbill (Alca torda) divides responsibility when raising its brood: both parents feed the chick with sand eels caught by diving.

GUILLEMOT EGGS

must return to land to breed and lay their hard-shelled eggs. Flight makes a range of coastal habitats easily accessible, including steep cliffs and rockfaces. On precarious ledges and among rocks – safe from non-flying predators – puffins, guillemots, gannets, and other birds gather to pair up and raise the next generation.

Colourful colonist In summer, the horned puffin (Fratercula corniculata) sports its breeding colours: its winter grey face becomes an immaculate white mask, and its bill turns yellow and bright red. Around north Pacific coastlines, horned puffins gather in colonies to nest on rocky cliffs. The densest colonies occur where there are plenty of crevices and cavities to shelter the eggs and chicks.

A dark fleshy “horn” projects above each eye in sexually mature adults, unlike in puffins of the North Atlantic

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Many birds depend entirely upon the ocean for food, but all

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cliff nesting

spotlight species

northern gannet With a wingspan of up to 1.8 m (6 ft), the northern gannet (Morus bassanus) is the north Atlantic’s largest seabird. A strong flier, this bird spends most of its life at sea, regularly making 540-km (336-mile) foraging expeditions; tagged birds have been recorded making even longer journeys. It soars over northwest Europe’s coastal waters year round, but its range extends

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from the southern Arctic to the Gulf of Mexico on a seasonal basis. Oily fish and squid comprise most of a gannet’s diet – herring, mackerel, and sprats are its preferred prey – but, as opportunists, these birds also steal any type of fish from nets and other seabirds. They often follow fishing boats far out to sea in the hope of feasting on discarded bycatch. More usually, the northern gannet stays closer to shore, flying above the water at heights of 10–40 m (33–130 ft) at an average speed of around 15 kph (10 mph). It searches the surface for schools of fish, identifying food sources by tracking dolphins or larger predatory fish. Some gannets hunt alone, but they typically feed in flocks of up to a thousand. When they spot their prey, hundreds plummet head-first into the sea, often from a considerable height, to grab a meal. Pairs of gannets mate for life, reinforcing bonds through behaviours

such as “mutual fencing” (knocking together of bills), and they return each year to nest in large, raucous colonies, known as gannetries. Although there are a few sites around North America, most northern gannets breed in 32 gannetries located between Brittany, France, and Norway that contain more than 70,000 breeding pairs. The female lays a single egg in late spring in a mounded nest of seaweed, feathers, and plant matter. Parents take turns incubating the egg by covering it with their feet, and they vigorously defend nests and young by stabbing intruders with their bills. Diving for food Gannets hunt by plunging into the sea beak-first, with their wings folded back, at speeds of up to 86 kph (53 mph). Most plunge dives are relatively shallow, but they can be as much as 22 m (72 ft) deep.

Rocky roost Gannetries are usually located on rocky coastlines, protected by the rugged terrain, like this one on the Shetland Isles. Although adult gannets have few natural predators, their eggs and chicks may be stolen by gulls, ravens, foxes, or weasels.

hopping on rocks For most seabirds that can fly, the journey between water and land typically presents few problems. But for flightless penguins, a rocky shoreline battered by waves is a constant challenge. Rockhopper penguins must brave the choppy waters as they dive for krill, and then – using little more than their clawed, webbed feet and willpower – scale the rocks on their return.

Vestigial hind toe does not reach the ground

Sole-walkers Penguins have plantigrade feet, which means that they walk on the soles of their feet, giving better traction. Other birds are digitigrade – they walk on their toes.

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Island penguin Southern rockhopper penguins (Eudyptes chrysocome), of the Falklands and other subantarctic islands, thrive on coastlines jagged with solidified lava, where they clear steep gullies in single jumps. The habitat, although harsh and craggy, provides shelter for the birds’ nests and pools of fresh drinking water that collect between the rocks.

Short, stout, bill, which is used for grabbing krill when diving, may also be used like a grappling hook when climbing steep slopes

Three forward-pointing toes have thick, strong claws that can grip rock; the toes are connected by webbing for surface paddling

Short, thick legs are powered by strong thigh muscles that help the bird to hop from rock to rock

PENGUIN POSTURE A streamlined body, with legs set far back, enables a penguin to cut through water like a torpedo. But adaptations that perfect swimming and diving leave a penguin ungainly on land. Compared with a gull, the legs of a penguin are lower down on the body, forcing the bird to stand more upright and giving it a waddling gait.

Stiff, flat, wings are held outwards for balance when jumping; they are used as paddles for propulsion when the bird dives

Spine is more vertical

Legs are lower on body

ROCKHOPPER PENGUIN SKELETON

Spine is more horizontal

Legs are higher on body

GREAT BLACK-BACKED GULL SKELETON

sandy beaches The shifting surface of a sandy beach is a difficult place to put down roots or dig a burrow, but it also presents opportunities. Flotsam arriving on a strandline attracts scavengers, and gently sloping beaches allow large, air-breathing animals to come ashore.

Making dunes Wind-blown sand gathers around plants and other obstacles to create dunes. With their deep network of roots, marram grasses stabilize dunes and enable them to increase in size.

Lines of new plants are produced from rhizomes that grow horizontally through the sand

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growing in wind-blown sand A sandy seashore exposed to gales can be a harsh environment for a plant: the salty wind dries tender shoots, and the sand it carries scours leaves and buries new growth. In these tough

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conditions, marram grasses not only survive – they thrive. They have wind-resistant leaves and a regrowth system that continually pushes the plants upwards from beneath rising piles of sand.

STIMULATED BY BURIAL Most short plants quickly get covered by shifting sand, but marram grass continually sends up vertical rhizomes (underground stems) from its rootstock and sprouts new green leaves above the sand’s surface. As more and more sand accumulates, the plant develops layer upon layer of additional roots higher in the sediment, which binds the sand together as the root fibres get thicker. Rhizomes Second-year root layer First-year root layer

GROWTH PATTERN OF AMMOPHILA ARENARIA AFTER BURIAL IN SAND

New leaves

Rootstock

Upper epidermis (surface layer of cells) is exposed to the wind, but it has a thick, waxy cuticle that reduces water loss from evaporation

Wind tolerance A cross section through common marram grass (Ammophila arenaria) shows how the leaf blade is rolled inwards, sheltering the stomata – minute pores that exchange gases for respiration and photosynthesis. The curled shape screens the stomata from the drying effects of the wind, while the central channel keeps moist air trapped close to more vulnerable, porous tissue layers.

Lower epidermis is rolled inwards and carries hairs to reduce air movement

Stomata (pores) for gaseous exchange are sunk at the base of pits, where they are less likely to lose water in the drying wind

Green mesophyll tissue contains the pigment chlorophyll, which absorbs light energy for photosynthesis

Ocean Surface (1983) In this masterwork of close observation and technical precision, Vija Celmins uses drypoint engraving, in which the image is incised into a plate using a sharply pointed tool, to recreate wave formations in her limited-edition monochromatic prints.

the ocean in art

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In the 20th century, a new art movement known as Photorealism emerged. This involved artists using a photograph as their primary visual reference to produce images that are so lifelike it is barely believable they have been created by the artist’s hand. This art form continues to evolve, with artists

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using the latest technologies. Among the most astonishing works are the super-realistic seascapes, with their almost tangible waves and sand. Inspired by Pop Art in the 1960s, the work of the first Photorealists in the 1970s was a commentary on the conflict between art and the explosion of photography in the 20th century. Artists projected the outline of a photograph onto canvas or paper, then demonstrated their extraordinary prowess in mimicking the textures and reflective surfaces of consumer culture icons, such as camping vans and sauce bottles, often using an airbrush. Here were banal subjects lacking any emotional depth presented with the technical skills of an 18th-century portrait artist perfecting the sheen on silks or the texture of fur. Since the early 1990s, technical advances in digital photography have taken Hyperrealism (as Photorealism is now more commonly known) into different realms. US artist Zaria Forman has flown with NASA survey missions over Arctic and Antarctic seas and has travelled to Greenland to photograph polar ice. In the Maldives, the lowest and flattest region on Earth, she photographed coastlines under threat as sea levels continue to rise. Her

message about the beauty and fragility of our world is writ large on vast canvasses of pristine ice masses and tropical waves. Each work captures a photographic moment in time and takes up to 400 hours to recreate. Latvian-American artist Vija Celmins also works on meticulous renderings of natural phenomena, such as waves, night skies, and the desert floor, often in sombre, dark grey tones. In the late 1960s, she produced highly realistic pencil drawings of the surface ripples in a small area of the Pacific Ocean; more recently, she has replicated those pencil strokes using an engraving tool to create remarkable prints.

My drawings celebrate the beauty of what we all stand to lose. I hope they can serve as records of sublime landscapes in flux. ZARIA FORMAN, TED TALKS LIVE, NOVEMBER 2015

Maldives No. 11 (2013) Zaria Forman conjures up mesmerizing waves lapping on a Maldives shore using only pastel crayons and her fingers and palms. Her giant canvases, produced from her own photographs of vanishing equatorial coastlines and melting ice in polar regions, reflect a planet in peril from climate change.

66 • 67 sandy beaches

Race for the sea Two baby loggerhead turtles (Caretta caretta) head for the ocean on Florida’s east coast. Most marine turtles hatch at night, when land predators are less likely to spot them. They scurry off in the most brightly lit direction – where moonlight or starlight reflects off the water – and away from the shadows of vegetation further inland.

nesting on beaches With their paddlelike limbs, marine turtles are superbly adapted to life in water, but their existence is not wholly divorced from the land. Their young, like those of terrestrial tortoises, hatch from hard-shelled, air-breathing eggs. The female turtles bury them on sandy beaches, but the strategy is not without risk. On exposed shores, hatchlings must brave land predators in the brief – but perilous – scamper to the sea. Females offset the certain loss by producing huge clutches, typically containing more than 100 eggs.

TEMPERATURE AND SEX The sex of a turtle embryo is determined by temperature: above 29°C (84°F), sex organs are more likely to become ovaries, producing females; below this, they develop as male testes. Buried eggs incubate as sunshine warms the sand, but the temperature inside the nest is not uniform – eggs buried deeper are slightly cooler. This temperature variation ensures that roughly equal numbers of females and males hatch.

Warmer top of nest produces more females

Cooler, deeper nests produce more males

Males more likely to hatch from eggs at bottom

SHALLOWER NEST

DEEPER NEST

Each turtle crawls beyond the reach of the tide to lay its eggs; the entire beach visit lasts about an hour

Natal rookery Female olive ridley turtles (Lepidochelys olivacea) return in their thousands to the beach nesting grounds of their birth, called rookeries. They use their hind legs to dig a hole in which to lay eggs, then bury the clutch and return to the sea.

Sculpted by the wind Barchan dunes form when the wind, coming predominantly from one direction, blows the sand into distinctive crescentshapes as on Isla Magdalena, on the Pacific coast of Baja California, Mexico.

beaches and dunes Beaches are zones where sediment in the form of sand – created by the action of rivers, cliff erosion, and transport from deep water towards the shore – accumulates before eventually being carried back to the sea by wave action. Beaches lose sand to the sea by the action of strong offshore rip-currents and winter storms. Sand may also be transported inland by wind to form dunes. The most important force for sand transport is persistent longshore drift, which drives a conveyor belt of supply

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and removal. The colour of sand varies according to the type of rock: grey-black from volcanic rocks; glistening white from coral and limestone; or golden, mainly comprising quartz coated with

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iron oxide.

TYPES OF BEACH Pocket and embayed beaches nestle in the more protected regions between headlands. Broad sandy beaches with gentle gradients are often flanked by dunes. Where wave energy is greater, sand is washed away and steep pebble beaches are built up. Where waves approach a shoreline obliquely, they move sand by a process of longshore drift and create sand spits, barrier islands, and sheltered lagoons. Lagoon Soft rock

Longshore drift

Hard rock Embayed beach Pocket beach

Sand spit

Wave direction

Aloft all hands, strike the top-masts and belay; Yon angry setting sun and fierce-edged clouds Declare the Typhoon’s coming. J.M.W. TURNER, UNTITLED POEM (1812) ACCOMPANYING THE SLAVE SHIP, 1840

The Sea of Ice (1823–24) The seascapes of German artist Caspar David Friedrich evoke awe in the natural world and a sense of human irrelevance in the face of an almighty power. Here a ship is crushed in its ice tomb, while the jagged ice is driven into pinnacles against the infinite blue of the sky.

the ocean in art

drama on the seas In the Romantic movement, which spanned most of the 19th century, neoclassical rules and norms to focus on their emotional response to the natural world and to the plight of individuals. Many iconic seascapes of the

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inspiration, originality, and imagination were key. Artists dispensed with

period, featuring towering waves and apocalyptic skies, tell contemporary

The Slave Ship (1840) In J.M.W. Turner’s celebrated work, the churning waves look as though they are on fire and the ship ploughs ominously into the storm as the captain carries out his evil mission. Turner’s full title, Slavers Overthrowing the Dead and Dying — Typho[on] Coming On, supplies the narrative for the carnage in the foreground: the flailing, shackled limbs of submerged slaves who have been thrown into the shark-infested sea.

The 19th-century French poet and art critic Charles Baudelaire described Romantic art as “precisely situated neither in choice of subject, nor in exact truth, but in a way of feeling.” For some artists, the freedom to work outdoors (made easier by the invention of paint tubes) fuelled a deeper engagement with land and sea. In studios, experimentation with brushwork, colour, and form fostered a range of individual techniques. Russian marine artist Ivan Aivazovsky conjured a sense of the ocean’s sublime magnitude with vast canvasses saturated with colour and light. In The Ninth Wave (1850) the rising Sun lights a huge wave that is threatening to engulf the survivors clinging to the wreckage of their ship. In a period when European colonialists were exploiting overseas territories, and scientists and explorers were sailing to remote regions, outrage and adventure surfaced in Romantic art. French painter Théodore Géricault’s The Raft of the Medusa (1819) is a striking recreation of the true story of crew and passengers abandoned

by officers when the French frigate Méduse ran aground on its way to Senegal. In this work, the deceased slip from a poorly made raft, survivors cling to life, and hope of rescue is encapsulated in a makeshift flag waved towards a brightening sky. More fancifully, English artist Sir Edwin Landseer imagined the outcome for Sir John Franklin’s failed attempt to find a Northwest Passage through Arctic seas. In his Man Proposes, God Disposes (1864) polar bears invade the ice-trapped wreckage to feed on human bones. A large proportion of the 19,000 watercolours and oils painted by the English artist J.M.W. Turner were seascapes. Over a lifetime he perfected washes of paint, textures, and bursts of light to create the natural phenomena of rain, fog, storm, sunrise, and sunset. He based his painting and poem The Slave Ship on the true story of the captain of the Zong, who ordered his crew to throw sick and dying slaves into the sea to guarantee insurance payments – a common practice in slave shipment.

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stories about human endeavour, disaster, and oppression.

spotlight species

american crocodile The American crocodile (Crocodylus acutus) exists in a range of habitats from freshwater rivers to brackish swamps and coastal waters, and is found in regions as far apart as Florida, USA and the Caribbean, as well as off

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both the Atlantic and Pacific coasts of South America. The American crocodile is one of the largest of the crocodile species; adults have an average length of 4.3 m (14 ft). Like all crocodiles, it has salt-secreting glands on its tongue that removes excess salt, helping it survive in higher salinities. The American crocodile has an especially large range of tolerance: most populations live in brackish lagoons, mangroves or estuaries, but others live in freshwater rivers and reservoirs much further inland. The largest Caribbean population – in the Dominican Republic – even succeeds in a salt lake with water that can be three times saltier than the ocean. A wide distribution across the American tropics is testament to the apparent adaptability of the American crocodile. The fact that it has colonized islands, including coral atolls, is proof that it often swims far out to sea, possibly aided by tidal currents.

While an American crocodile’s jaws can exert hundreds of kilograms of pressure when it bites, easily crushing an adult turtle shell, they can also be very gentle. Females can pick up and carefully squeeze unbroken eggs to help the young crocodiles hatch, and they often carry their young in their mouths to transport them to the water. A crocodile’s coneshaped teeth are designed for grabbing and holding prey but not for chewing. They are constantly being replaced, and an animal may go through 8,000 teeth during its lifetime. Adapted for hunting A crocodile senses prey by smell and via sensory bumps on the sides of its jaws that detect vibrations. They can swim open-mouthed and have excellent vision; a transparent third eyelid protects the eye when the animal is submerged.

SURVIVING UNDERWATER A crocodile’s mouth is not watertight, so to prevent water flooding its lungs and gut when underwater, a palatal valve – a large flap behind the tongue – seals the entrance to the windpipe and gullet. At the same time, smaller nostril valves close the nose. In this way, a crocodile can stay submerged without breathing for over an hour, and it can even open its mouth wide enough to grab or manipulate prey. The raised position of the open nostrils also allows the crocodile to breathe air while swimming or hanging just below the water surface.

Nostril Nasal passage Palatal fold Gullet, or oesophagus

Tongue Palatal valve Windpipe, or trachea

CROSS SECTION OF A CROCODILE’S THROAT

beachcombing A sandy beach can provide a good living, even for animals that never enter the water. Each tide brings a deposit of natural flotsam, in the form of seaweed. This, in turn, attracts swarms of flies, beetles, and tiny crustaceans: food for shorebirds, such as plovers. Up beyond the ocean’s reach, among the sparsely vegetated dunes, birds build their nests with sticks, stones, shells, and anything else they might collect as they forage along the water’s edge.

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Life above the tides Along the southern Australian coastlines, the hooded plover (Thinornis cucullatus) prefers beaches strewn with plenty of seaweed. Its legs are too short to wade for its food, so it sticks to the strandline when foraging for invertebrates.

Large eyes help the bird to spot small prey among the tideline debris

Disguised egg clutch The bird’s speckled eggs resemble the surrounding pebbles. The nest may be lined with seaweed and shell fragments for additional camouflage. Once hatched, the sandy-coloured chicks blend in too.

NESTING TOGETHER Even when partly concealed by the spoils of beachcombing, the nests of hooded plovers are vulnerable to predation. Being territorial breeders, hooded plovers prefer to nest over 20 m (66 ft) apart. Ground-nesting birds often breed in loose colonies, typically with mixed species for extra vigilance, and hooded plovers may be joined by pied oystercatchers (Haematopus longirostris).

The hooded plover’s nest is a shallow depression called a scrape

PIED OYSTERCATCHERS

Seaweed fronds detached by wave action attract kelp flies and other decomposers, providing a ready source of food for birds

Coastal devastation The aftermath of the 2004 tsunami that ravaged the west coast of Aceh, Indonesia, pictured in 2005, testifies to the destructive power of this ocean event over wide tracts of the formerly tree-covered shoreline.

tsunamis Tsunamis are unusual waves of extreme wavelength (up to 200 km/125 miles) that can travel across an entire ocean at a speed of up to 800 kph (500 mph). A common cause of tsunamis is the sudden vertical movement of the seafloor due to earthquakes or giant submarine slides under the sea. They may also be caused by events on land that deposit vast amounts of material into the sea, such as avalanches, landslides, volcanic eruptions, or the calving of large icebergs from ice-sheets or

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glaciers. In each case, the enormous volume of ocean water displaced gives a tsunami its huge power and velocity. Tsunamis can originate in any ocean but are most common in areas of

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frequent volcanic activity.

FROM UNDERSEA SHOCK TO COASTAL DESTRUCTION A tsunami often starts with a sudden displacement of the ocean floor, which causes a large movement of water that produces a long, low, almost imperceptible wave in the open ocean. The wave’s height increases dramatically as it crosses the shallow continental shelf and sweeps towards land, forming a giant wall of water – up to 30 m (100 ft) high – that surges inland, wreaking havoc along the coast. Water elevated above fault

Direction of wave Wave reaches maximum height near coastline

Shockwave created by sudden displacement of seafloor along fault line

Wave compressed as it reaches shallower water

estuaries mudflats and

The world’s muddy shorelines and estuaries are home to animals that can burrow in sticky mud and to plants and animals that can withstand the constant changes in salinity that accompany the rise and fall of the tide.

living in sediment

The foot can extend up to 6 cm (2.5 in) as it burrows

Among the invertebrate animals that live in mud are many kinds of bivalve: molluscs with a two-part shell, such as clams and cockles. They use their gills to filter particles of food, including the organic detritus and microorganisms that typically enrich the seafloor. Many bivalves use their muscular foot to burrow into the substrate, away from surface predators. Surrounded by sediment, these molluscs then draw water through their body to extract both oxygen and nourishment.

Burrowing bivalve A prickly cockle (Acanthocardia echinata) pushes its muscular foot into the sand. The foot then expands near its tip to achieve traction, before pulling the rest of the cockle’s body beneath the surface.

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Crenulated edges of valves interlock when shell closes

The hinge of the shell is surrounded by a flat platform shaped like the deck of a ship, inspiring the name “ark shell”

SIPHONING WATER Water does not easily circulate through sticky mud, so many burrowing bivalves use siphons to draw water down from the surface. The siphons extend when the valves open. Those with the longest siphons can burrow the deepest. Cockles, with short siphons, and ark shells, which lack siphons, live closer to the surface.

Waste water flows out through exhalant siphon

Water is initially drawn in through inhalant siphon

Anus Intestine Gills collect food and oxygen Palps pass suitably sized food particles to the mouth

CROSS SECTION OF COCKLE FILTER-FEEDING IN MUD

Fleshy foot is powered by multiple muscles that extend the foot or move it from side to side when burrowing

Burrowing foot

Hinged shell Like other bivalves, the Indo-Pacific blood clam (Tergillarca granosa) from tropical coastal muds has a shell made of two parts, or valves, connected by a hinge of tough ligament. The valves are pulled shut by muscles when danger threatens. As these muscles relax, the shell gapes open, enabling the mollusc to extend its muscular burrowing foot and circulate water for filter-feeding.

Ripples in the sand As the tide retreats on the Scottish Hebridean island of Eigg, the action of the water moulds the fine sand into distinctive ripples. The metallic sheen of the sand is the result of its high content of volcanic material.

tides The regular – usually twice daily – rise and fall of sea level, known as the tide, has been a constant phenomenon since the oceans first formed four billion years ago. Tides are waves with very long wavelengths that sweep around the planet, moving up and down the low-lying coastal zone, with dramatic effect on life in the shallows. High tides are the crest of the wave, and low tides are the trough. The difference in height between high and low tides

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is termed the tidal range. This varies from less than 1 m (3 ft) to just over 16 m (53 ft). Tides are caused by the combined effects of the gravitational pull of the Moon and Sun and the rotation

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of Earth and the Moon.

MONTHLY CYCLES The influence of the Moon’s gravitational pull is greater than that of the Sun. Ocean water is pulled into a bulge on the side facing the Moon, while centrifugal force creates an equal bulge on the opposite side of Earth. When the Sun and Moon are aligned, the tidal bulge is at its maximum (the spring tide). When they are at right angles, the tidal bulge is at its minimum (the neap tide). Sun

Gravitational pull

Sun

New Moon

High tide Low tide

Low tide on Earth

High tide Full Moon

SPRING TIDES NEW MOON

High tide

Low tide

First quarter Moon

Last quarter Moon Low tide

High tide

NEAP TIDES FULL MOON

LAST QUARTER

NEAP

SPRING

NEAP

NEW MOON TIDE HEIGHT

FIRST QUARTER

SPRING

SPRING

seabed stinger

Sand is whipped up by stingray feeding

While some sea animals use venom to attack prey, many fish sting only in self-defence. Stingrays, which are cartilaginous fish related to sharks, spend their time resting on the seafloor and hunting prey in the sediment. In this position, with their mouth on the underside, they are vulnerable to attack from above. If they perceive a direct and inescapable threat, for example when trodden on, they lash their barbed tail upwards and deliver their venom.

Feeding in the sand When a stingray hunts, it fans its fins and squirts jets of water from its mouth in order to dislodge its prey (small fish and invertebrates) buried in sediment on the seabed.

Pointed fin-tips give a diamondshaped outline

WHIP AND BARB The narrow tail of a stingray can be moved at whiplike speed. When the stingray strikes, the tail flicks forwards over the head to stab the target with a serrated spine, which produces venom and is encased in a sheath. The spine may break, but it can regrow within several months. Serrated edge of spine Spiracle

Whiplike tail Eye

Winglike pectoral fin

STINGRAY (UPPER SIDE)

Sheath

Pair of venom glands in two grooves in spine underside Light coloration of underside provides camouflage, making the stingray harder to see from below

Lying low Like all rays, the southern stingray (Hypanus americanus) is dorsoventrally flattened, with a low profile suited to life on the seabed. The mouth is on the underside to enable it to feed in the sediment. To prevent sand clogging the gills, water is taken in via spiracles on top of the head. These draw in water, which is passed over the gills and expelled from its gills on the underside.

Nostril provides excellent sense of smell

Row of gill slits expel water from the body

Mouth on underside so ray can feed on seabed

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Spiracles on top of head enable stingray to breathe when lying on seabed

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Small spines on midline

LETHAL VENOM Stonefish are the world’s most venomous fish, although they use their sting defensively rather than for hunting. Stored in a pair of venom glands, the poison is delivered via 13 modified dorsal fin spines. These act like hypodermic needles to inject a cocktail of toxins that attack a victim’s muscles, nerves, blood cells, and cardiovascular system, causing agonizing pain, shock, paralysis, and severe tissue damage.

Opening obstructed by sheath

Pressure applied to spine from above triggers sting Venom released

Sheath Venom duct in spine

Punctured sheath

Pair of venom glands

Venom in glands activated

Connective tissue

PRIMED

DELIVERED

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Engulfed in an instant The chief hunting aids of the reef stonefish (Synanceia verrucosa) are its prominent eyes and large mouth, the outlines of which are disguised by highly textured skin. When the stonefish spots its prey, such as smaller fish or crustaceans, its mouth opens in less than a fiftieth of a second, creating suction that prey are powerless to resist.

concealed danger Scorpionfish and stonefish are ambush predators, but unlike stargazers (see pp.232–33) and anglers, which use a lure to tempt prey closer, they rely purely on camouflage and an ability to remain perfectly still for hours at a time. Some scorpionfish and stonefish species are able to change colour to match their background, and each fish appears to Skin is highly textured and sometimes carries algae, which may attract herbivorous prey closer to the stonefish

select resting places that best match their individual coloration.

Dorsal fin contains spines that deliver venom

Hiding in plain sight Lurid pink, orange, and purple are not obvious camouflage colours, but set against the complex background of a coral reef, a reef stonefish can remain invisible to prey and predators until it moves. Despite their camouflage and venom, small stonefish are occasionally eaten by predators such as sea snakes, sharks, and rays.

Large pectoral fins and tapered tail are often shuffled under sediment or tucked into crevices, making stonefish even harder to spot

Prominent eyes increase field of vision

Large mouth, which is fringed with warts and tassels, has an upwardprotruding jaw; the mouth expands rapidly to engulf prey above

Elongated snout, which resembles the blade of a saw, is an extension of the skull

Skeleton is made of cartilage instead of bone

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Saw-teeth are evenly sized, flat, and peglike, with a sharp point

Nostrils positioned on underside of head A side-to-side sweeping motion is used to detect buried prey

Sweep and slash A sawfish uses its saw-like snout in several ways: to scan the seabed for electrical signals from prey hidden in the sand, to swipe at and disable its prey in open water, and to thrash at an assailant or sometimes at other sawfish when competing for food.

sensing electricity Sharks, rays, and skates are known for their extraordinary sense of smell, but they also possess an electroreceptive sense located in pinhole-sized pits on the snout. These pits are especially abundant on the enlarged snouts of hammerhead sharks, sawsharks, and sawfish. The latter are actually rays and only distant cousins of sawsharks. Their similar-looking “saws” are examples of convergent evolution, whereby different species have evolved similar traits in order to adapt to the same environment.

SENSORY PITS Sawfish teeth Like all sawfish, the smalltooth sawfish (Pristis pectinata, shown here as an X-ray) has a long, narrow snout (rostrum) and two sets of teeth. The most obvious are the large, robust, sharply pointed saw-teeth, which are found all along the snout. In addition, the mouth contains a set of tiny, blunt teeth, arranged in 10–12 rows, which are used for crushing prey.

Sharks and rays detect electrical activity in the muscles of their prey using jelly-filled pits, known as ampullae of Lorenzini, on their snout and around their mouth. Each pit has a neural connection to the brain, which creates an electrical picture of the surroundings.

SAWFISH (UNDERSIDE)

Skin is covered in small placoid scales; these form a tough protective layer and help to reduce drag in the water

Snout covered in sensory pits Nostril Mouth Gill slits

Pectoral fin

Epidermis of skin Canal containing plug of mucus transmits electrical charge Dermis of skin Electroreceptor cells detect the stimulus of the electrical charge Sensory nerve fibres carry electrical impulses to the brain

migrating to breed Young eels turn from yellow to silver as they enter rivers

Many fish return to the place where they began life in order to breed. In doing so, they increase the likelihood that their offspring will have similar success. For salmon, which spend most of their adult lives at sea, the return journey to their home rivers and streams is particularly challenging. First, they undergo physiological changes to enable them to reacclimatize to fresh water. During the upstream journey, which can cover hundreds or even thousands of kilometres, they have to battle swift currents and leap waterfalls, usually without feeding. The strain of the journey combined

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with hormonal changes lead to programmed death within days of spawning.

Migrations in reverse While salmon are anadromous, migrating upstream to spawn and die, freshwater eels are the opposite (catadromous): they begin life at sea, migrate to fresh water, and return to sea to breed.

BODY CHANGES Salmon undergo many changes in their life history. Newly hatched “fry” develop camouflage markings in the form of vertical bars (the “parr” stage), and as the fish prepare for life at sea (the “smolt” stage) they turn silver. The oceanic phase lasts up to five years, then salmon change colour again – to brown, red, or green, depending on the species – before they return to fresh water. Breeding males of several species undergo changes in shape, most notably the pink salmon (right).

Silvery scales and a torpedo-shaped body (both sexes)

OCEANIC PHASE

Turns brown; body shape remains similar

BREEDING FEMALE

BREEDING MALE

Develops distinct hump and hooked jaw (kype)

Homing instinct Salmon rely on two main senses to navigate their way back to their spawning grounds. An ability to detect Earth’s magnetic field leads them to their home river, then they use their acute sense of smell to find the gravel bed where they hatched. Here, pink salmon (Oncorhynchus gorbuscha) in Alaska, US, are heading upriver to breed.

BILLS FOR PURPOSE Having different bills with different uses reduces competition for food among shorebirds – even between related species, such as sandpipers. Long, pointed bills – curved or straight – can penetrate deep into thick sediment in search of invertebrate food. Shorter bills are more useful for foraging near or at the surface of the intertidal mud.

mud probing Many shorebirds, including members of the sandpiper family, breed around the Arctic tundra. As the days shorten and insect food dwindles, they fly south to overwinter on

Asian dowitcher (Limnodromus semipalmatus) probes the mid depths

Spoon-billed sandpiper (Calidris pygmaea) sweeps bill from side to side

Ruddy turnstone (Arenaria interpres) flips surface objects to find animals underneath

Depth (cm)

150 200

long-distance journeys and sustains them through the winter probing bill – to secure a meal.

Terek sandpiper (Xenus cinereus) probes shallower depths THICK MUD

SOFT, WET MUD

Far eastern curlew (Numenius madagascarensis) probes deep burrows for crabs and worms

BILL ADAPTATIONS IN EAST-ASIAN SANDPIPERS

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diet of mud-dwelling invertebrates, which helps to fuel their months. Each species is equipped with the perfect tool – a

50 100

intertidal mudflats around the world. Here they enjoy a rich

Switching diets After catching fly larvae and beetles during the Canadian summer, the short-billed dowitcher (Limnodromus griseus) migrates southwards and repurposes its bill for probing, as it hunts for mud-burrowing worms, molluscs, and crustaceans along coastlines of the American tropics.

The horny sheath around the bill is honeycombed with cavities containing pressure sensors, which enable the bird to detect the movements of buried prey

Shorter bill may be better for catching insects

Age-related bills Like others of the sandpiper family, the insect-eating chicks of the black-tailed godwit (Limosa limosa) hatch with proportionately shorter bills than those of mud-probing adults.

Slender head may be plunged part-way into the mud when foraging, helping the bill to reach deeper for burrowing invertebrates

Brown-grey plumage may offer some camouflage from predators when viewed against the ground, both when breeding in subarctic meadows and when feeding on mudflats

Flying the flag (1660–80) Celebrating trade in the Dutch Golden Age, this unnamed work by marine artist Abraham Storck depicts merchant ships and galleons at anchor in a tranquil fantasy port. It is a counterpart to another Storck work, Dutch Ships for a Port in the Mediterranean Sea.

A Dutch Ferry Before a Breeze (1640s) A red-sailed ferry carrying passengers and goods across a blustery bay showcases Simon de Vlieger’s draughtsmanship and command of the atmospheric effects of waves and weather.

the ocean in art

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the dutch golden age Riding the crest of a wave in the 17th century, the Dutch rose to great power through their mastery of the sea. Their unparalleled boat- and shipbuilding

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skills for transportation, trade, and war were matched by a prolific output of great art in every genre. The works of marine artists were especially popular, capturing the might of galleons, the passage of small vessels on inland waters, and the atmospheric effects of weather, sea, and sky. In 1640, merchant and traveller Peter Mundy counted 26 trade ships arriving at the Dutch Texel Inlet from distant shores and concluded that nowhere in the world came near to it for traffic and commerce by sea. Art, he noted, was a prerequisite in even the poorest homes and in the stalls of butchers, bakers, and blacksmiths. Current-day estimates suggest that between 1640 and 1660 Dutch artists produced more than 1.3 million pictures. Paintings of huge fleets and merchant

ships in foreign ports reflected Dutch maritime and economic dominance. Major works, such as Abraham Storck’s The Four Days’ Battle (1666), showing fighting in the Anglo-Dutch war, reflected constant naval activity to keep trade routes open. Other artists, including Jan van Goyen, Ludolf Backhuysen, and Willem van de Velde the younger, depicted coastal sailing and the quiet harbours, fishing inlets, and winter skating intrinsic to Dutch domestic life.

As For the art off Painting and the affection off the people (of the Netherlands) to Pictures, I thincke none other goe beeyond them... PETER MUNDY, THE TRAVELS OF PETER MUNDY IN EUROPE AND ASIA, 1608–1667

In the pink As with flamingos and the scarlet ibis, the pink coloration of the roseate spoonbill (Platalea ajaja) comes from carotenoid pigments that are found in its food. The intensity of colour varies according to age, season, and location, and the availability of carotenoid-rich prey.

Head and neck become bald in adult birds

Throat and oesophagus are elastic to accommodate prey, which is swallowed whole

Plumage ranges from white to deep crimson

sweeping for food For birds feeding in murky water, it is often difficult to see beneath the surface. As a result, several species have evolved a sensitive bill that enables them to detect food in shallow waters, without relying on their sense of sight

Orange bill of young spoonbills fades to grey in adult birds

– an adaptation that also allows them to continue feeding at night. All six species of spoonbill hunt by “tactolocation”, detecting small fish, shrimps, and aquatic insect larvae and plant matter in lagoons, pools, and estuarine waters up to 30 cm (12 in) deep.

Early days Young spoonbills start life with a short, straight beak. This elongates rapidly in the days after hatching, begins to broaden at the tip after one to two weeks, and attains the characteristic adult shape after about one month.

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Broad-tipped bill has a touch-sensitive lining and snaps shut to trap larger prey

A spoonbill feeds in shallow water, sweeping its partially open bill in a side-to-side or circular motion to create a vortex. After dislodging food from the bottom, it traps the catch between its broad mandibles, lifts its head, and claps its bill shut, crushing its prey before swallowing.

Fine combs sieve tiniest food items from water

Closed bill has gap, allowing water to drain

lower mandible

Flattened mandibles

Bill widens towards the downwardcurved tip

SPOONBILL FEEDING

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FEEDING TECHNIQUE

Tail helps the osprey to manoeuvre into position, so that the bird can accurately hit the target

Wings pull back in W-shape, helping the osprey to cut through the air when diving towards the water’s surface

Preparing for splashdown Ospreys plunge from heights of 40 m (130 ft) on long, narrow wings. This wing shape is ideal not only for diving but also for hovering over large bodies of water while selecting a suitable target.

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Feet swing forwards, ready to grab the fish, just before the bird impacts the water

fishing with feet Raptors – birds of prey, such as eagles and hawks – typically catch their quarry with talons that pierce the prey’s flesh. The osprey (Pandion haliaetus) is the only daytime raptor that feeds almost exclusively on fish. It hunts like other raptors, meaning that it dives feet first – but it does so mainly in saltwater habitats. Once its target is properly gripped, the osprey is capable of flying back to its perch carrying a fish half its body weight.

CATCHING SLIPPERY PREY Raptors usually have an arrangement of toes with three pointing forwards and one pointing back – like most types of bird. This helps with perching as well as gripping prey. But slippery, wriggling fish need a firmer grip, so the osprey has a reversible outer toe, allowing two talons to hook either side of a catch. Smaller fish can be held with one foot, but heavier ones are secured using both feet, one in front of the other.

Normal position of outer toe

Outer toe twists backwards to get a firmer grip

OSPREY FEET

Dense, oily plumage keeps the feathers waterproofed when diving for fish Bill has a long, sharp hook that is able to penetrate the tough, scaly skin of large fish

Toes carry spiny pads on their undersides, which enable the feet to cling tightly to a fish

Coastal raptor Despite having long legs to help reach for fish, an osprey’s natural buoyancy means it cannot penetrate more than about 1 m (3 ft) under water. It therefore catches surface-dwelling fish in shallow bays and along shorelines. This technique is successful worldwide: the osprey is one of the most wide-ranging of all bird species, found in the Americas, Africa, Eurasia, and Australasia.

mangroves salt marshes

and

These tidal habitats are dominated by trees and other true plants that have adapted to life in salt water. They also protect shorelines from coastal erosion and provide homes to diverse communities of other living things.

growing in salt marshes

Maturing shoots turn violet-red with betacyanin, the same pigment found in beetroot

Plants that grow on land or rooted in fresh water rely on salts in their tissues to pull water up into their leaves: water tends to seep towards higher salt concentrations by a process called osmosis. Plants of intertidal marshes, such as sea-blites, are specially adapted to the saltier conditions, typically with fleshy leaves that accumulate the extra salt needed to keep drawing in water.

Bicoloured shoots Sea-blites, such the Australian Suaeda australis, turn from green to red as they build up betacyanin – a pigment that protects cells in the salty conditions.

GAINING AND LOSING WATER Plants adapted to salty conditions are called halophytes. By concentrating salt in their tissues – at higher levels than in their surroundings – they absorb water by osmosis, from lower to higher salt concentration. Conventional land plants, known as mesophytes, have lower salt concentrations than sea water, so they lose water by osmosis in salty conditions.

SALT CONCENTRATION Normal soil

Inside mesophyte

Salty soil

Inside halophyte

Plant gains water by osmosis

MESOPHYTE ON NORMAL SOIL

MESOPHYTE ON SALTY SOIL

Plant gains water by osmosis

Plant loses water by osmosis and wilts

HALOPHYTE ON SALTY SOIL

Salt marsh annual In China’s Liaohe River delta, conditions are too wet and salty for most types of plant to survive. But the Eurasian sea-blite (Suaeda salsa) thrives in abundance. It grows from seed each year, and during autumn its shoots gradually transform the shoreline into a spectacular red “beach”.

Colourful colonists Colonizers of mangrove roots include bluebell tunicates (Clavelina). Where sunlight can reach, photosynthesizing green algae thrive alongside them.

The tunicates’ bottleshaped bodies draw in water to filter out food particles

A colony of tunicates arises because each individual can produce neighbouring clones

Along muddy shorelines around the tropics, mangrove roots growing like pillars in the water often provide the only solid surface in the intertidal habitat. As a result, they are quickly colonized by opportunistic algae underwater “gardens” are a mixed blessing: they nourish the roots with their waste but also smother the pores through which the roots breathe.

Underwater garden Submerged under nutrient-rich waters at high tide, these mangrove roots are all but hidden by plankton-feeders such as tentacled polyps and bottle-shaped tunicates. Colonists that grow faster may have the advantage, but some can produce chemicals that repel their neighbours.

TUNICATE LIFE CYCLE Tunicates, like many ocean invertebrates, have a life cycle that alternates between being attached and being free-swimming. As sedentary filter-feeders, they trap food particles from sea water circulating through their soft bodies. Their non-feeding larvae are supported by a firm rod called a notochord. This structure is anatomically equivalent to a backbone – evidence that tunicates are more closely related to vertebrates than to other invertebrates.

ADULT TUNICATE Notochord

Nerve cord

METAMORPHOSIS

LARVA

SPERM AND EGGS

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and animals. Competition for space is intense. For the mangrove, these

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colonizing roots

growing on stilts

Salt crystals form when saline water secreted by leaf glands evaporates

A plant that grows into a tall tree benefits from reaching more light than its shorter neighbours. But the extra weight involved in scaling such heights needs strong support. On muddy tropical shores, salt-tolerant trees called mangroves manage on the soft ground by distributing their weight over a wide area with stiltlike roots or with buttress roots that spread horizontally along the ground. This stops the trees from toppling, even when their bases are submerged by the incoming tide. The high, arching stilts also collect vital oxygen, enabling the trees to thrive where the sludgy ground is not

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easily aerated and keeping the root tissues alive far below the surface.

Coping with salt Mangroves can tolerate high levels of salt in their tissues. Some species exude excess salt from their leaves, which become coated with white salt crystals.

ROOTS THAT BREATHE In order to distribute oxygen, mangrove roots are honeycombed with air-filled spaces. Air enters the roots at high tide through pores called lenticels, but the roots’ shape varies between species. Unlike the stilt-rooted Rhizophora mangroves, the roots of Bruguiera emerge from the mud as a series of loops, whereas Avicennia mangroves reach the air through pneumatophores – root tips that grow upwards from the mud’s surface, effectively acting as snorkels.

RHIZOPHORA ROOTS

Roots form arching stilts Loop roots poke up through mud

Snorkel-like root tips

BRUGUIERA ROOTS

AVICENNIA ROOTS

Shoreline thicket The stilt-based architecture of mud-growing mangrove trees provides a unique forest habitat along tropical coastlines around the world. In southern Asia, the arching roots of the red mangrove (Rhizophora mangle) are home to small foraging animals as diverse as crabs, mudskippers, and lizards – and even to monkeys and birds.

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Brown-coloured symbiotic algae are concentrated in the oral arms; by swimming upside-down, the jellyfish exposes the algae to sunlight

living upside-down Living in mangrove-fringed lagoons and in seagrass beds – often gathering by the hundreds – is an unusual jellyfish that lives upsidedown, with its stinging arms waving upwards in the water. Settled on the bottom in the sunlit shallows, it relies on brown-coloured algae peppering its flesh to make food by photosynthesis. Food made in this way supplements the nutrients the jellyfish derives from its captured prey.

Seabed jelly The Indo-Pacific upside-down jellyfish (Cassiopea andromeda) pulsates its bell and flickers its arms in the clear, warm water. The arms are multipurpose: as they move back and forth through the water, they absorb oxygen, trap food, and expose their food-making algae to the sunlight.

Inverted bell Like more conventional jellyfish, Cassiopea uses the pulsating action of its bell for propulsion, but it can do this with its arms facing upwards or downwards. Oral arms are packed with stinging cells that can paralyse small prey; they may also release mucus-coated balls of stinging cells into the water The bell is encircled by muscle fibres that contract to cause the bell to pulsate

Branching oral arms have frilly tips that give them a cauliflowerlike appearance; the tips of the arms are punctured with multiple tiny mouths

The coloured streaks on the bell, which itself can be up to 30 cm (12 in) in diameter, vary from brown to blue

RHIZOSTOME JELLYFISH Cassiopea belongs to a group of jellyfish called rhizostomes, meaning “root-mouthed”. Instead of true tentacles and a single mouth, rhizostomes have oral arms that carry all the stinging cells as well as tiny mouths. The mouths open into channels that work much like roots, collecting food particles and passing them to the stomach for digestion.

Oral arm with multiple mouths Bell

RHIZOSTOME Tentacles around rim of bell

Single mouth

Oral arm

MOON JELLY (“TYPICAL” JELLYFISH)

living fossil Horseshoe crabs appeared in the oceans half a billion years ago, when the jointed-legged arthropods were diversifying via evolution into insects, arachnids, and crustaceans. Ancient, fossilized horseshoe crabs are very similar in shape to those alive today, suggesting that these animals have changed little over millions of years of evolution. Despite their name and their hard shell, they are more closely related to spiders than to true crabs.

Stiff, tail-like telson is used as a rudder to help steer when swimming

Ancient survivor The mangrove horseshoe crab (Carcinoscorpius rotundicauda) and its relatives belong to an ancient group that includes extinct giant water “scorpions” known as eurypterids. Their shared body plan – a fused head and thorax, a separate abdomen, and a shieldlike carapace – dates from the dawn of invertebrate evolution.

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Carapace is stiffened with a tough material called chitin, but it is not hardened with minerals like the brittle shell of a true crab

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TOP VIEW

Hinge between the front part of the body (fused head and thorax) and the rear part (abdomen) helps the animal flex across the middle

BOTTOM VIEW

A pincer (chela) on the end of each walking leg is used for grabbing prey and passing it forwards towards the mouth

Grinding plates called gnathobases at the base of the legs break up prey into pieces tiny enough to fit inside the small mouth

UNCHANGED BY TIME The stability of some ocean habitats may help explain why evolutionary change in certain groups seems minimal. Lingula brachiopods (shelled animals that burrow in sediment) could be the least altered of all animals. Fossil shells from the Cambrian Period, 540 million years ago, are virtually identical to shells of modern-day Lingula. Males cling to females as they fertilize thousands of eggs that are then buried in sand

Mating horseshoe crabs Atlantic horseshoe crabs (Limulus polyphemus) gather in huge numbers to breed along shallow sandy coastlines – much like their ancestors did millions of years ago.

LINGULA BRACHIOPODS

Seeing salt The Dead Sea, an inland sea between Israel and Jordan, has an average salinity of about 34 per cent. The high rate of evaporation leads to the fomation of visible deposits of salt.

salt water The first oceans that formed on Earth some four billion years ago contained little salt, but were weakly acidic as a result of gasses released by volcanic activity. But today, as a result of dissolution of minerals from the land and the seafloor, the oceans contain over five trillion tonnes of salts from nearly 100 different elements. The concentration of salts in the oceans is between 3.3 and 3.7 per cent. Salinity is greater in warm, semi-enclosed seas such as the Mediterranean and the Red Sea. The two main components of magnesium, sulphur, calcium, and potassium. If the oceans evaporated completely, salt residues would be equivalent to

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of ocean salts are sodium and chlorine, with smaller amounts

a layer 45 m (150 ft) thick over the entire planet.

In the chemical balancing act that maintains the salinity of the oceans, elements from mid-ocean ridges, volcanoes, and dissolved in rivers are balanced by the removal of salts by living organisms and the deposition of their remains on the seafloor. Some salts are also removed by chemical changes (mineralization) and by incorporation of sediments into the substrate as a result of shifts in the seafloor. Clouds of volcanic ash Dust blown off land

Rivers carry minerals to the sea

Minerals from seafloor incorporated into landmass

Spread of volcanic ash into rain clouds Volcanic ash falls into the sea

Rain washes volcanic dust and gases into the sea

Deposition of salts from marine organisms Uptake of salts by marine organisms

Minerals released by volcanic activity

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THE SALT CYCLE

Eyes on stalks allow the crab to see signals and threats from further away

Showing off Male crabs that have larger claws and an impressive waving display are more likely to attract a mate. It takes a strong male North American red-jointed fiddler crab (Minuca minax) to grow and wield a heavy appendage, but some males appear to gamble by growing impressive-looking lightweight claws that are actually too flimsy for fighting.

Smaller claw of male is used for feeding

Walking legs lack pincers

Waving claw, present only in males and used for attracting a female, threat displays, and fighting; can be on left or right side

CRUSTACEAN APPENDAGES Crabs, shrimps, lobsters, and crayfish are classified as decapod crustaceans, which all have a segmented body and one pair of appendages per segment. Decapod means “ten legs”, referring to four pairs of walking legs and one pair that bears the claws. Other appendages serve as antennae, for collecting sensory information, and mouthparts. Crabs differ from other decapods in carrying their abdomen tucked under their body rather than extended behind them.

Eyestalk

Mouthparts

Claw

Walking legs

Abdomen

CRAB (UNDERSIDE)

waving crabs and females, a phenomenon known as sexual dimorphism. The males are often equipped with outsized claws (chelae), used for fighting and social

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Many species of crab exhibit pronounced differences between males

signalling, including threat displays and courtship. Most fiddler crabs live can be seen from relatively long distances. Males dig breeding burrows and wave from the entrance to attract passing females. Before mating, the male plugs the burrow from inside to keep rivals out and protect the female and her eggs. She emerges when her offspring are ready to hatch into the sea.

Female advantage The female fiddler crab uses both claws for feeding, unlike the male, which uses just one. The female is therefore able to pick up food twice as fast.

Female claws are small and symmetrical

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on flat expanses, such as sandy beaches and mudflats, where visual signals

hunting above water

Archerfish can leap up to twice their 30 cm (12 in) body length above water

In bankside waters, including mangrove swamps, many predatory fish supplement underwater prey with targets on overhanging vegetation above the surface. Some leap vertically upwards to catch an insect, but archerfish also use a second tactic: they spit a jet of water to topple the target. They are remarkably accurate – even in rippling, cloudy waters. Their lightning-fast speed means they can

Archerfish can strike prey on low-hanging leaves by launching their whole body out of the water. This energetic hunting method can often be more successful than shooting prey.

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also grab the prize before nearby competitors even see it fall.

Jumping for prey

Large eyes provide acute vision, even in the low light of densely shaded mangrove swamps

AIM AND REFRACTION When preparing to shoot at prey, archerfish align their body according to the angle of the target above the water. They make an adjustment for refraction – the bending of light that makes objects above or below the water appear to be in a slightly different position when viewed from the other side of the interface. Perceived position of prey Actual position of prey

Refracted light

ARCHERFISH SCRUTINIZING PREY

Large caudal fin provides thrust, aiding rapid acceleration towards prey

Upturned mouth can suck fallen prey from water surface

Learning curve Young banded archerfish (Toxotes jaculatrix) hunt in shoals and appear to learn by watching others. They often make several attempts to dislodge their prey, and their accuracy improves with practice.

Impression, Sunrise (1872) Claude Monet’s hazy view of the port of Le Havre, in Normandy, is credited with giving rise to the name of the Impressionist movement. Awash with colours against a vague backdrop of ships and buildings, the work was vilified when it was exhibited in Paris in 1874.

Étretat. The Cliff of Aval (1890) A Normandy seascape by Eugène Boudin features his characteristic luminous skies and tranquil waters, but also the striking arch of rock made famous by his pupil Claude Monet.

the ocean in art

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impressions of the sea Claude Monet is often regarded as the father of the Impressionist movement. In his later years, he paid tribute to the artist who taught him how to paint the

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sea. In 1858, Monet was an 18-year-old caricaturist from Normandy, France, when he first met Eugène Boudin, 20 years his senior. Boudin introduced the young Monet to the naturalistic approach of painting “en plein air” (outdoors), where he learned to absorb and capture the atmosphere of the coast. Boudin was a master of expansive seascapes, skyscapes, and tranquil scenes of gentlefolk picknicking and promenading along the shore. Monet took on board his friend’s advice that he should “learn to appreciate the sea, the light (and) the blue sky”, but he went on to develop his own Impressionist techniques to portray the dramatic Normandy coastline. His focus was on capturing the colours of shadows in different lights, eliminating black to create a more vibrant effect. He painted the arch of rock called the Manneporte

at Étretat up to 18 times, using quick dabs from loaded brushes to fix a ray of light or a cloud, and layering different tints while still wet instead of mixing colours. In his journals, the French writer Guy de Maupassant describes Monet on the beach in Étretat in 1886, switching between five or six canvases as the light changed throughout the day. On one occasion, writes Maupassant, “he took a downpour beating on the sea in his hands and dashed it on the canvas – and indeed it was the rain that he had thus painted …”

A landscape is only an impression, instantaneous, hence the label they’ve given us. CLAUDE MONET, INTERVIEW FOR LA REVUE ILLUSTRÉE, 1889

Many marine animals – such as jellyfish, crustaceans, and starfish – have salt levels in their bodies that change, or conform, with their surroundings. Other animals, including most vertebrates, keep their salt levels constant: they regulate. Both conformers and regulators can survive the changing salinity in an estuary. The conformers tolerate extremes of salt inside the body; the regulators resist this from happening.

FRESH WATER Relative salt concentration in blood

CONFORMERS AND REGULATORS

OPEN OCEAN

ESTUARY Red dots indicate the limits of salt tolerance (beyond which the animal dies)

Salt levels inside a conformer 0

Salt levels inside a regulator

5 10 15 20 25 30 35 Salt (parts per thousand) in surrounding water

SALINITY IN CONFORMERS AND REGULATORS

40

adapting to changing salinity Salt levels in the open ocean are relatively stable, at around 35 parts per thousand. The influence of fresh water added by rivers has little effect, except near the coasts. Most ocean organisms – just like those in freshwater habitats – are so adapted to the water Tears produced by lachrymal glands contain a high concentration of salt; the glands secrete excess salt when the turtle gets dehydrated

around them that they cannot survive changes in salinity: they are described as stenohaline. In estuaries, where salt levels fall and rise with the tides, life is euryhaline: it tolerates fluctuating salinity.

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Horny beak is used to crush prey such as fish and marsh snails

Foot pushes backwards against the water for thrust

Skin is cornified (thickened) with plenty of reinforcing protein called keratin, which helps to reduce absorption of excess salt or water

Balancing body salinity The only claw-footed turtle to thrive in estuaries, the diamondback terrapin (Malaclemys terrapin) has tough skin to resist the variable salinity and tear glands to secrete excess salt. If its salt levels rise, it spends more time in fresh water, avoids the saltiest prey, and lifts its head to drink directly from the fresh water of falling rain.

Clawed, webbed feet Like freshwater turtles and terrapins, the diamondback has clawed feet, rather than flippers, for walking on the ground or estuary sediment. Webbing between the toes helps with propulsion in the water.

coral reefs Among the most complex and beautiful of Earth’s ecosystems, reefs are built by colonial animals. These massive structures are home to diverse, colourful communities of organisms, many of which have become highly specialized to find their own niche.

Bottle colony The filter-feeding “bottles” of an Indo-Pacific blue sponge (Lamellodysidea chlorea) are connected in a sprawling colony. In coastal seas murky with sediment, Lamellodysidea sponges can smother living corals – and may come to dominate a reef.

Didemnum sea squirt grows as a brightly coloured, filter-feeding colony – either vivid green or pink – on almost any available surface, including the bodies of sponges

An opening, called an osculum, at the top of each bottle-shaped chamber releases water that has been filtered of food

The chamber walls are peppered with cells that carry pores; each pore, called an ostium, allows water to enter the sponge

simple bodies Oceans are home to the simplest animals – sponges. Some animals in this group can grow into giants more than 1 m (3 ft) across, but in all of them – no matter what the size – their constituent cells are so loosely connected that if the entire body is fragmented, each piece may retain its ability to develop into a new individual. Nevertheless, just as in other animals, the cells cooperate to keep the entire structure alive. They help to circulate water through the porous sponge to extract suspended food.

Fragile skeleton grows at great depths

Barrel sponge, the largest type of sponge, can reach 1.8 m (6 ft) in diameter

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DEMOSPONGE Clathrina grows as tangled tubes

Types of sponge A sponge’s supporting skeleton is made of different possible materials: fibres of collagen (a protein) or hard spicules (mineral needles). Demosponges, generally the softest sponges, are typically dominated by collagen, while glass and calcareous sponges are supported, respectively, by silica or calcite spicules.

BODY ORGANIZATION The different kinds of cell that make up the body of a typical sponge are organized around porous, bottlelike chambers. Collar-flagellate cells in the body lining have beating hairs that maintain water flow: in through the walls and out through an opening at the top. Each hair sits within a permeable collar that traps particles of food carried in the water stream.

CALCAREOUS SPONGE

Water outlet (osculum)

Collarflagellate cell Pore cell

Opening (ostium) in pore cell admits water

Outer casing cell Defensive cell Skeletal unit (spicule)

CROSS SECTION OF TYPICAL SPONGE

coral reefs

GLASS SPONGE

Each polyp carries a ring of tentacles for catching plankton; polyps at the ends of coral branches have six tentacles, those on the sides have twelve

Epidermis (surface skin) of the coral contains brown-pigmented algae called zooxanthellae, which supplement the coral’s nutrition through photosynthesis

Each branch of the coral is supported by a rocky core that makes up most of its bulk

making rock Some animals affect their surroundings more profoundly than others. Many corals use minerals from sea water to construct rocky skeletons that accumulate over hundreds – or even thousands – of years, producing the most celebrated of all ocean features: the coral reef. The living coral persists as scarcely more than a thin veil with tiny plankton-catching tentacles. But the rocky foundation it has made can be a kilometre (half a mile) thick and stretch for hundreds of kilometres across the seabed.

BUILDING A REEF

Mouth of polyp A branching skeleton has a large enough surface area to support many thousands of polyps in life

Tentacle

Corallite (skeleton of single polyp)

Underlying rock

SINGLE POLYP

A thin surface epidermis secretes materials to make the skeleton Skeleton builds up to form a non-living framework

Dead coral Stripped of living tissue, this white coral skeleton is virtually pure calcium carbonate – a chalky mineral made by the coral’s living layer.

CORAL REEF

coral reefs

Microscopic planktonic coral larvae settle onto rock, where they develop into polyps. Each polyp, no bigger than a grain of rice, builds a tiny, cup-shaped rocky skeleton, known as a corallite. Over time, more interconnected polyps are generated as the colony expands outwards on the surface, while the skeleton beneath thickens – by about 0.5 cm (¼ in) per year – to become the rocky foundation of a reef.

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Coral branches The branches of a stony coral (Acropora sp.) colony consist of a hard, rocky core clad in a “skin” that carries tentacled polyps. Nutrients harvested from trapped plankton are shared around the polyp colony by the skin.

synchronizing spawn

Gamete bundle emerges from mouth of polyp

Sexual reproduction for most types of ocean animals involves broadcasting sex cells into open water and relying on chance that fertilization will happen. For corals, separate patches of the same species must synchronize their spawning so that sperm and eggs are released at the same time. Environmental cues – such as a seasonal rise in temperature or phases of the Moon – trigger one of the most spectacular reproductive events on the planet: when a reef bursts with clouds of coral spawn. It has been

coral reefs

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estimated that a million eggs come from each square metre of reef.

Reproductive polyp Most corals are hermaphrodites: the polyps in their colony eject round gamete bundles that break apart into sperm and eggs within about half an hour of their release.

CORAL SEXUAL LIFE CYCLE Corals and related anemones have a life cycle dominated by the sedentary polyp: a flask-shaped animal with stinging tentacles for catching planktonic prey. Colonies of coral polyps release their gamete bundles in synchrony to maximize the chances of fertilization. Each fertilized egg develops into a tiny, flat-bodied planula larva, which mixes with the drifting plankton. If it survives the attention of predators, the larva eventually settles on the seabed and transforms into a polyp. It then multiplies asexually to form a new coral colony.

Polyps release gamete bundles

Bundles split into eggs and sperm for fertilization

GAMETES

Planula beats microscopic hairs to swim

PLANULA LARVA

CORAL COLONY

Stinging tentacles

Polyp grows attached to the seabed

POLYP

Releasing gametes In some reefs around the world, all corals spawn simultaneously, but in the Red Sea, species vary in their spawning season. This species of Acropora coral spawns in early summer on the night of a full Moon, releasing pink bundles of gametes by the billion.

Epithelium (surface skin) secretes the gorgonin, which forms the solid inner core that supports the colony The base of each polyp connects with neighbouring polyps through channels called solenia, which share nutrients through the colony (see p.132)

Eight-tentacled polyps illustrate the eight-fold symmetry that is characteristic of sea fans and other types of octocoral

Skin colour varies between colonies of this species: some are yellow instead of red

Dichotomous branching, by which a branch repeatedly splits in two as it grows, produces a fan shape that is effective at capturing plankton over a wide area

Growing across the current Sea fans typically grow in one plane that is perpendicular to the direction of the current, ensuring that their fan shape is in the best position for trapping drifting plankton.

horny skeleton The best-known corals are those that lay down the huge rocky foundations of a reef. But related animals build colonies in a different way. Sea fans grow branches supported by a core of hornlike protein called gorgonin. They stretch upwards from the seafloor or horizontally as they suspend over steep drop-offs

VARIED SUPPORT Sea fans belong to a group called octocorals, so named because their polyps carry eight tentacles. Support structures in octocorals are more diverse than in the stony, six-tentacled hexacorals. Some, the soft corals (see pp.132–33), lack any hard skeleton at all. Gorgonians, which include sea fans, are supported by horny material called gorgonin, while the organ-pipe coral (Tubipora musica) is reinforced by chalky minerals.

on the outer edge of a reef. Here, far below the ocean surface, they use their tiny polyps to trap plankton.

STRUCTURE OF ORGAN-PIPE CORAL

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Branches of the deep A single branch of the colourful sea rod (Diodogorgia nodulifera), from the Caribbean, is covered with plankton-trapping polyps. Unlike many stony corals growing near the surface, this sea fan contains no light-absorbing, photosynthesizing algae, so it is able to grow in the dark depths.

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Polyps can retract if danger threatens, or extend their tentacles when catching plankton

Polyps containing photosynthetic algae cover the “mushroom’s” cap, where they are exposed to light

Soft-bodied coral

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Soft corals lack the hard, rocky skeletons of reef corals. Some, such as the rough leather coral (Sarcophyton glaucum), form giant, fleshy, mushroom-shaped colonies.

living in a colony Colonial animals are common in the ocean. A mature coral consists of thousands of tiny, anemonelike polyps. Each polyp

coral reefs

uses its stinging tentacles to catch plankton but is linked to its neighbours so that nourishment is shared. All the polyps develop from the same fertilized egg and are genetically identical, and the entire colony functions like a single superorganism. By spreading over a wide area, the colony can maximize its catch of food as well as the number of eggs it is able to release during spawning.

Fleshy colony Dozens of polyps pack just a thumb-sized area of a Sarcophyton leather coral. As well as catching plankton, each polyp is packed with photosynthetic algae, from which they gain extra nutrients. The polyps project from a mass of fleshy tissue called coenenchyme.

SHARING NUTRITION Each coral polyp has a gut cavity that ingests planktonic food and ejects undigested waste. Nutrients from digested prey are spread throughout the colony. In stony corals, this occurs in the thin “skin” overlying the rocky skeleton. In soft corals, canals called solenia penetrate deeper into the fleshy colony to share the food.

TYPICAL SOFT CORAL STRUCTURE

Tentacles surround mouth

Canals linking gut cavities share food between polyps

Gut cavity

Mass of fleshy tissue lacks any hard skeleton

Stony corals Also known as hard corals, these are the architects of the world’s coral reefs. True stony corals have rigid skeletons made of calcium carbonate – in the form of a mineral called aragonite – and each polyp sits in its own protective cup, called a corallite. In areas with strong waves these colonies develop into robust mounds or flattened shapes; in sheltered seas, the same species can form more intricate shapes with delicate branching patterns.

Large, thick branches resembling elk antlers provide shelter for many reef species

Dense groups, or thickets, up to 2.4 m (8 ft) across and 1.2 m (4 ft) high form in shallow waters

STAGHORN CORAL Acropora cervicornis

Soft corals Also known as octocorals because their polyps have eight tentacles, these corals are soft and bendable. Often treelike in appearance, these non-reef-building colonies are supported by hornlike cores and protected by fleshy outer rinds.

ELKHORN CORAL Acropora palmata

Treelike species found in deep waters of the North Atlantic and the Barents Sea

Stiff, bushlike colony grows in a single plane

CARNATION CORAL Gersemia fruticosa

GORGONIAN SEA FAN Subergorgia

Flexible, fleshy branches enable coral to tolerate buffeting by strong ocean currents

Eight-tentacled polyp captures passing plankton to obtain nutrients

Fleshy and flexible Commonly known as the Kenyan tree coral (Capnella imbricata), this branched soft coral emerges from a single “trunk” that is fixed to a rock. The colonies inhabit coastal shores and rocky reef slopes and can grow to around 45 cm (18 in).

Large polyps branch in many directions, and tentacles extend to catch passing zooplankton

Long, meandering valleys in dome each contain several polyps

Horizontal plates are formed of tiny branchlets that grow vertically and horizontally

Vertical, cylindrical columns up to 3 m (10 ft) tall grow from an encrusted base

TUBE CORAL Tubastraea coccinea

PILLAR CORAL Dendrogyra cylindrus

BOULDER BRAIN CORAL Colpophyllia natans

Open polyps ready to consume prey; they close before eating again

Red branches are edged with white polyps and move with ocean currents

TABLE CORAL Acropora cytherea

Fingerlike “branches” are covered with retractable polyps

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GORGONIAN SEA WHIP Ellisella ceratophyta

coral reefs

Base, or peduncle, anchors in sand or mud in shallow waters

SEA PEN CORAL Pteroeides

MUSHROOM CORAL Anthomastus

corals Corals are found in all the oceans of the world, but reef-building species are found mainly in shallow tropical and subtropical seas. Coral is formed from huge colonies of individuals called polyps that feed on plankton. Colonies that live in shallow, warmer waters host zooxanthellae, which use carbon dioxide from the coral’s respiration in photosynthesis and, in turn, pass nutrients back to the coral.

SPAGHETTI FINGER LEATHER CORAL Sinularia flexibilis

Green concentrations of zooxanthellae are found in the polyp’s column, which contains the gut cavity

Transparent, jelly-packed tissues help to transmit light to zooxanthellae in the gut lining

Algae in the flesh When a single coral polyp is magnified, the zooxanthellae are visible as spots of green-coloured cells. Each cell has light-absorbing chlorophyll – the same pigment found in photosynthesizing plants.

powered by sunlight Animal flesh is nourished by food that has been digested and assimilated,

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but some types of marine animal are partly solar powered. Many corals and some hydrozoans, anemones, sponges, and molluscs contain photosynthetic algae called zooxanthellae. These grow and multiply in the animal’s sunlit tissues and use carbon dioxide from its respiration to make

coral reefs

food, much of which passes to the host and is key to healthy growth.

Skeleton from photosynthesis Millepora fire hydrocorals – named for their painful sting – are colonial hydrozoans with hard skeletons, like those of true stony corals. Their dependence upon symbiotic zooxanthellae restricts them to brightly lit shallow water. They use much of the food gained from the algae’s photosynthesis to build their chalky skeletons.

ZOOXANTHELLAE The zooxanthellae of marine animals belong to a group of algae known as dinoflagellates. These have free-living forms that swim with whiplike structures called flagella, but when swallowed by coral polyps, they lose their flagella and become cysts in the Chloroplast performs photosynthesis

polyp’s gut lining. A natural yet vulnerable balance exists between the swimming and encysted forms. Warming of the sea is leading to a net loss of cysts, bleaching corals and often killing them.

Swimming dinoflagellates swallowed by polyp

Some encysted forms are ejected as they develop into swimming (sexual) forms Chloroplast Encysted form in gut lining

Flagellum

SWIMMING DINOFLAGELLATE

CORAL POLYP

ENCYSTED DINOFLAGELLATE

Solar-powered mat Like some other anemones, Haddon’s carpet anemone (Stichodactyla haddoni), of the Indo-Pacific, supplements nutrients from its prey with food produced by algae growing in the flesh of its wide oral disc. The algae use energy from sunlight penetrating the water to photosynthesize and make sugar, which they share with the anemone.

The longer tentacles of many anemone species can reach further to overcome large prey

Stinging tentacles

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Anemones vary in the potency of their venom. Most trap tiny planktonic animals, but some, such as this dahlia anemone (Urticina felina) are able to immobilize bigger prey, including urchins.

Knoblike ending of each short tentacle is coated in nematocysts (stinging cells)

stinging for prey For an animal that is attached to the seabed, an anemone is a surprisingly efficient predator: a fleshy column, or polyp, crowned with stinging tentacles reaches up into the water to catch passing animal prey. The tentacles bring the paralysed victim to the mouth at the centre of the polyp, which swallows the meal into the digestive cavity below. Carpet anemones are among the largest polyps of a tropical reef: a single oral disc, covered in short, budlike tentacles, can span nearly 1 m (3 ft).

FIRING VENOM Anemones, along with corals and jellyfish, are cnidarians. These soft-bodied predators owe their stinging capabilities to unique cells, called nematocysts, in their skin. Each nematocyst contains a capsule of venom and a barbed thread like a miniature harpoon. Contact with prey triggers the harpoon to fire, penetrating the victim with a chemical cocktail that can paralyse muscles.

Tube carries venom into wound

Triggering bristle Closed lid

Bristle deflected by touch

Spine Barb

Inverted tube with thin, coiled end

Open lid

Cell nucleus

Cell nucleus

UNDISCHARGED NEMATOCYST

DISCHARGED NEMATOCYST

Fleshy oral disc surrounds a central mouth and contains contracting muscle fibres that raise its carpet of stubby tentacles upwards into the water – and closer to prey

Muscular column contains a gut cavity that digests prey and absorbs nutrients

coral reefs Reef-building corals live in shallow tropical waters, where the sea-surface temperature ranges from 20° to 35°C (68° to 95°F). They need a rocky surface on which to build, normal marine salinity, and waters that are free from excess sediment. Vast populations of tiny coral polyps – individuals are often no larger than a pea – work together with a host of other organisms to construct and maintain the largest living structures on Earth. The Great Barrier Reef off northeastern Australia, which comprises over 3,000 separate reefs, is even visible from space. Coral reefs are highly sensitive to changes in their ocean environment and are gradually dying as a result of rising temperatures, ocean acidification, and reduced oxygen levels.

Rich pickings As dusk falls, shoals of epaulette soldierfish (Myripristis kuntee) emerge from the cover of a reef in Palau. Their big eyes help them hunt through the night on planktonic animals, such as crab larvae.

CORAL ATOLL FORMATION In the open ocean, coral atolls originate where reef organisms have constructed a fringing reef around the shores of newly formed volcanic islands. When volcanic activity ceases, the island subsides due to a Newly formed volcanic island

Coral grows along shoreline

Lagoon

Island subsides Lagoon

1. FRINGING REEF

combination of plate movement and weathering. The reef on its flanks continues to grow upwards, first becoming a barrier reef – separated from the land by a lagoon. Later the island disappears, resulting in the formation of an atoll – a ring of coral islands with no central landmass.

Barrier reef forms as coral continues to grow

Coral reefs form island chain

2. BARRIER REEF

Coral continues to grow

3. ATOLL

PASSING ON POISON

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Some animals that eat zoanthids, such as crustaceans, seem to tolerate their poison. Many ocean toxins get passed along food chains in this way. Ciguatera syndrome in humans is caused by eating fish that contains high levels of ciguatoxin – a poison produced by algae called dinoflagellates. This poison is not excreted after the algae are consumed, so its concentration rises to potentially lethal levels in consumers higher up in the food chain – including fish served up on diners’ plates.

This microsopic alga grows on seaweed and other algae, and produces ciguatoxin

200 picograms of ciguatoxin per gram of herbivorous fish

Toxic dinoflagellate (Gambierdiscus toxicus)

Juvenile damselfish

Tropical sunlit coastlines around the world can be gaudy with

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Adult snapper

BIOACCUMULATION OF TOXINS IN THE OCEAN FOOD CHAIN

blooming with poison colourful zoanthids. Like anemones, these animals produce large, soft polyps. Like corals, they grow in colonies – although they lack a hard, reef-forming skeleton. The biggest zoanthid polyps resemble mesembryanthemum flowers, but their striking colours may serve as a warning of their toxicity. Many zoanthids harbour bitter chemicals called alkaloids that are poisonous and deter grazing animals. At least some of these poisons may be derived from planktonic organisms trapped by the zoanthid’s tentacles.

Lethal pigment A zoanthid obtains both its colour and its poison from alkaloid chemicals known as zoanthoxanthins. The alkaloids produce the vivid blue and green of the tentacles, but they are also toxic to nerves and muscles in other animals. Also present – but hidden by the alkaloids – are photosynthetic algae that provide the zoanthid with extra food.

1,000 picograms of ciguatoxin per gram of carnivorous fish

Blue base of the tentacles carries a different form of the alkaloid pigment compared with that in the green tips

Tentacles may fluoresce due to the colourful alkaloid: some of the light absorbed by the chemical during the day is emitted at night, producing a greenish glow

Radioles (side-branches) of each palp have beating cilia (microscopic hairs) that waft particles of food towards the mouth

The operculum is a modified, disc-shaped palp that is used to plug the entrance to the worm’s tube for protection when the animal withdraws inside

The calcareous tube is strengthened by a triangular ridge running along the top

Coral-living worm The palps of a star fan worm (Pomatostegus stellatus) spread out in the shape of a horseshoe. They are packed with oxygenabsorbing pigment and lined with food-collecting hairs. The rest of the worm lives inside a calcareous (chalky) tube buried within the rocky skeleton of a tropical stony coral.

The hard tube of Spirobranchus lamarcki, a European relative of the star fan worm, is visible – typically attached to a stone, rock, or occasionally the carapace of a crab.

fanning the water Of the thousands of species of marine annelid (segmented) worms, many their cousins on land. Other marine annelids can swim through open water. But some, called fan worms, live in tubes, compromising their ability to swim or burrow away from danger. A fan worm’s front end reaches out into the water, where a crown of fingerlike structures, called palps, sweeps the water for oxygen and particles of food. When danger threatens, the body uses retractor muscles to pull the exposed parts completely inside the tube.

TYPES OF TUBE Fan worms called serpulids, such as the star fan worm, build hard, chalky tubes made from calcium carbonate secreted by glands in the collar around the base of their palps. Other types of fan worm – the closely related sabellids – build soft, membranous tubes made from mucus mixed with sediment collected by the palps.

Hard shell is fused to rock or stone on one side

Soft tube is partially buried in sand or mud

SPIRORBIS (A SERPULID)

SABELLA (A SABELLID)

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use their muscular bodies for burrowing in sediment – just like earthworms,

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Pink hue of palps comes from blood pigments in their tissues; the pigments chemically bind to oxygen and extract it from water for respiration

Exposed tube

Water purifiers There are more than 10,000 species of marine bivalves. All are filterfeeders, able to remove contaminants from sea water; an oyster can filter 95 litres (25 gallons) a day.

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spotlight species

giant clams to the coral reef. These heavyweight molluscs bask in the tropical sunlight of the Indian and Pacific oceans from east Africa to the Pitcairn Islands.

Like other bivalve molluscs, a giant clam has a shell formed of two valves, connected by a hinge. It contains zooxanthellae – a type of algae – that photosynthesize and make 90 per cent of the clam’s food. The remainder of its nutrition comes from filter-feeding plankton. In some species, the fleshy mantle is vividly coloured with pigments or reflective crystals, which help to screen ultra-violet and other potentially harmful radiation. Just like food-making algae in coral, the giant clam has a mutually beneficial relationship with the zooxanthellae as the clam passes carbon dioxide and nitrogen Patterned giants The smooth giant clam (Tridacna derasa) of barrier reefs and island atolls, is the second largest species, growing to 60 cm (24 in) long, and has a particularly brilliant mantle pattern of blue or green.

compounds that are needed to make nutrients into the zooxanthellae. This symbiosis is productive: a record-breaking specimen of Tridacna gigas, the largest species, weighed half a tonne. Like so many other iconic animals on the reef, giant clams help to engineer the complex community around them. Over time, their shells are colonized with life, while many animals – from crustaceans to fish – live over the mantle, some as parasites. Zooxanthellae occasionally expelled from the mantle may provide food for plankton-eaters too. Giant clams are hermaphrodites, but release most of their sperm before their eggs to reduce the chance of selffertilization. Like most other molluscs, the fertilized eggs develop into tiny larvae that swim in the plankton, before metamorphosing into adults and settling on the ocean bottom.

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Giant clams (Tridacna) are the biggest non-colonial animals that grow fixed

The cloud of ink contains chemical irritants that help to repel predators

Poison alert The vivid colours of a variable neon sea slug (Nembrotha kubaryana) are aposematic, meaning that they act as a warning signal to predators. This Indo-Pacific species has toxic slime, which comes from eating a particular type of sea squirt – a soft-bodied, filter-feeding animal of the seafloor.

Defensive ink When disturbed, this sea hare – a kind of sea slug – releases a cloud of acrid purple ink. The ink is partly derived from the sea hare’s diet of algae.

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collecting weaponry Soft-bodied molluscs lacking hard shells need alternative forms of protection against predators. Many sea slugs equip themselves with defences acquired from their food. Some graze on toxic organisms and harbour the poisons to ooze their own noxious slime or eject repelling ink. Others eat the stinging tentacles of jellyfish or anemones and preserve the stingers (nematocysts), which become incorporated into their bodies yet remain fully capable of firing.

STORING STINGERS The variable neon sea slug belongs to a group of sea slugs called dorids, which have a plume of gills and rely on toxic slime. Another group, the aeolids, store stingers from their prey in each fingerlike projection, or ceras (plural: cerata), on their back. The microscopic stingers ingested with their food are transported through side-branches of the gut and held in the cerata tips, ready to fire when a predator attacks.

Anus

Gut

Rhinophore

Gills Mouth

DORID SEA SLUG Cnidosac at tip of ceras stores stingers

Anus

Gut side-branches transport stingers Rhinophore

Mouth

AEOLID SEA SLUG

Tentaclelike sense organ, called a rhinophore, tastes the water and can detect sea squirt prey Orange markings help reinforce the colourful warning of the animal’s toxicity, but some equally poisonous individuals of this variable species are only green and black

Plumelike gills, arranged in a circle, absorb oxygen from the surrounding water

Quick change Octopuses that are more active in sunlight than at night are the best colour-changers, and the aptly named day octopus (Octopus cyanea) is the champion, being recorded switching 1,000 times over a seven-hour period. It uses black stripes when courting and turns dark when hunting.

PIGMENT CONTROL Colour changing in many animals – including octopuses and other cephalopods – is achieved by specialized skin cells called chromatophores. Each chromatophore contains a pigment, the colour of which is revealed when it disperses from a central point. Cephalopod chromatophores are especially complex, being controlled by tiny muscles that dilate a pigment-containing sac to spread the colour – all triggered by nerve impulses voluntarily fired from the brain. Muscle cells are relaxed

Pigment granules

Muscle cells contract

Sac dilates

Granules spread out

PALER SKIN COLOUR

DARKER SKIN COLOUR

Each arm carries two rows of stalked suckers that can grip prey and other objects

Shape-shifting Like other soft-bodied octopus species, the day octopus can change its shape as well as its colour. By spreading its body and casting a shadow over lurking prey, it may encourage a shadeloving crab to venture further from its hiding place.

Slit-shaped pupil splits light into its constituent wavelengths, enabling the octopus to detect different colours, even though its eyes lack the colour-sensing cells found in other animals with colour vision

Spreading the arms helps the connecting webbing cast a larger shadow False eye spots may direct predators away from the most vulnerable body parts, but their exact function is unknown

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Interbrachial web – a stretch of skin connecting the base of the eight arms – is packed with colour-changing cells (chromatophores)

changing colour Where sunshine penetrates the sea, many animals flaunt colours, and some even change colour when their behaviour alters. The switch can occur rapidly because it is controlled by lightning-fast nerve impulses. Cephalopods, such as octopuses and cuttlefish, are among the most impressive colour-changers. Within seconds, an octopus sensing danger can blend in with the seabed and vanish, or, spotting a potential mate, impress with bold patterns.

Marine science for the masses (1850s) An issue of the popular illustrated Parisian magazine Le Magasin Pittoresque includes a delicate wood engraving of named species of bivalves, sea snails, and a sea slug in a project to educate the wider population about marine life.

the ocean in art

art meets science Natural history illustration came of age in the 19th century in response to need for accurate representation of specimens. The sea was a new frontier for exploration, and the complexity and vibrancy of its myriad life-forms was both a challenge and an inspiration to the artists recording them.

Nudibranchs (1899–1904) Crossing the boundaries between scientific illustration and art, Ernst Haeckel’s nudibranchs (soft-bodied marine gastropods) are remarkable for their detail and harmonious arrangement.

Ocean Life (1859) An idealized assembly of 75 vibrant sea creatures and corals from a variety of geographical zones was created by physician and naturalist James M. Sommerville to illustrate his pamphlet Ocean Life. Art professor Christian Schussele’s watercolour for the lithograph has all the hallmarks of a still-life painting.

Britain’s HMS Challenger returned from a four-year voyage around the world in the 1870s, with samples trawled from many different ocean depths and new data on the chemistry of sea water, currents, sea temperatures, and the geology of the seafloor. One of many enthusiasts fired up by the findings was German doctor and zoologist Ernst Haeckel. His major work Kunstformen der Natur features 100 stunning lithographs that reveal the symmetry and beauty of the ocean’s smallest life-forms. A ground-breaking 1855 study of the Atlantic by US naval officer Matthew Fontaine Maury inspired naturalist James M. Sommerville to commission a dazzling watercolour illustration of its species.

The grouping may be considered, rather as an intellectual truth than as a literal view. It might be termed a mental oasis of the sea... JAMES M. SOMMERVILLE, INTRODUCTION TO OCEAN LIFE, 1859

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Describing sea creatures was historically challenging as specimens rapidly lost their colours and shrank after being preserved in alcohol. The Zoological Society of London’s solution was to use art painted in situ. From 1812, tea merchant John Reeves spent 19 years in Macao, where he commissioned Chinese artists to create detailed paintings of fish. Many of these paintings became iconotypes: the basis for the description of a new species.

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public fascination with voyages to formerly remote regions and a scientific

cleaning hosts

Cleaner shrimp may enter the host’s mouth to pick food from its jaws and teeth

Sunlit coral reefs are fertile, physically complex places with a rich biodiversity. As a result, more species evolve to be specialized in what they do, reducing competition in such a crowded habitat, and many are driven into close relationships. Shrimps that once scavenged for food now pick parasites and dead skin off living hosts and even advertise their services at cleaning stations. In this mutually beneficial symbiosis, visiting fish “clients” are cleared

Colourful cleaner On coral reefs in the Indo-Pacific, the distinctive red-and-white pattern of the scarlet skunk shrimp (Lysmata amboinensis) – named for its stripes – may serve as a visual signal to fish at cleaning stations. Several species of skunk shrimp act as efficient fish cleaners in tropical waters around the world.

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of potentially harmful pests, while the cleaner shrimps get a meal.

Red stripes are caused by a chemical pigment called astaxanthin in the crustacean’s carapace

Cleaning the hunter Some cleaner shrimps form strong bonds with moray eels. By sharing the eel’s lair, they get some protection from predators.

Long white antennae may be waved around as part of the visual signal that advertises the shrimp’s cleaning behaviour to a “client” fish

CLEANER FISH Fish from groups as diverse as gobies and wrasses have independently evolved cleaning behaviour on coral reefs. Like cleaner shrimps, they consume skin parasites, and most share a similar striped colour pattern, the stripes often being blue or dark. Their cleaning station is typically a conspicuous seabed feature, such as a coral outcrop. Here, “client” fish gather and may solicit the attentions of waiting cleaners through their posture or swimming movements.

BLUESTREAK CLEANER WRASSE (LABROIDES DIMIDATUS)

Large eyes are used to spot “clients”; in dim light, shrimps may be more wary of approaching potentially dangerous predators and exaggerate their pre-cleaning signals, such as leg rocking and waving antennae

Legs rock the body from side to side when approaching a shrimp-eating “client”, helping to reinforce the cleaning intent and avoid accidental attack by a predator

Under cover The spider decorator crab (Camposcia retusa) is so devoted to staying hidden that the only parts of its body not covered by debris and living things are those it uses to collect the masking material – its pincers.

making a mask Although crabs can famously use their pincers in self-defence, many species adopt a less confrontational approach: they wear a disguise. By plastering their body with flotsam or cuttings – anything from scraps of seaweed to colonial animals like sponges – they can blend in with the seabed. Much of what they wear keeps on growing, becoming a living mask that improves the deception over time.

Slender pincers have sharp cutting edges for snipping pieces of algae or sponge

Body debris includes fragments of seaweed, sponges, small stones, and shells collected by the crab

Hooked hairs grow in bunches, which provides a stronger grip when holding debris

Velcro crab The body of the spider decorator crab is covered in hook-tipped hairs. The hooks work like Velcro, securing objects to the body transferred there by the pincers.

CRAB DÉCOR Some crab collectors are specialists. Those of the family Dromiidae camouflage themselves with sponges. They have hooked rear legs for transferring a sponge to the back of their shell. Pom-pom crabs (Lybia) even use décor with a sting: they carry tiny anemones (Triactis) in their pincers to ward off predators.

Sponge in place on crab’s back

Anemones held by pincers

POM-POM CRAB

SPONGE CRAB

Brightly coloured sponges may produce noxious chemicals that repel any predators not fooled by the disguise

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Yellow or red sponges stay alive and keep growing when attached to the crab

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The legs, as well as the body, are covered in hairs, so practically the entire crab can carry debris

Fleshy projections (papillae) cover the body

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Anus serves as both an exit for excreted waste and an inlet for oxygenated water required for respiration

Sharing resources The thorny sea cucumber (Colochirus quadrangularis) lives in sunlit waters to about 115 m (380 ft) deep. When feeding, it rears upwards and spreads its tentacles to trap food suspended in the water. Some of the food may also be taken by tiny shrimps living in among the tentacles.

seabed feeding

Tentacles carrying food are inserted one by one into the mouth

Animals that live sedentary or slow-moving lives on the seabed make the most of the food that comes to them. Suspensionfeeders trap particles of living or dead material from the water, using bristles or tentacles. Detritivores specialize in dead material, known as detritus, which can be trapped in the water or gathered from the seabed. In deep water, detritus raining from above replaces sunlight as the main source of energy.

Feeding tentacles The reef-dwelling sea apple (Pseudocolochirus violaceus) is a colourful sea cucumber that uses frilly tentacles to trap tiny particles, such as algae, zooplankton, and dead material, from sunlit shallow water.

Body is flexible and muscular

Feathery feeding tentacles trap particles of food

WHALE FALL Detritivores recycle matter and energy back into the food web. A dead whale first provides food for mobile scavengers, including sharks and hagfish, then slower ones like sea pigs (a type of sea cucumber), then colonists such as worms and crustaceans. When the flesh is gone, communities of bacteria in the bones produce hydrogen sulphide and use it in place of sunlight to fuel the manufacture of carbohydrate (see p.262).

Worms and crustaceans Scavengers eat the soft tissue

Invertebrates feed on the remains

Mussels, clams, and tube worms drawn to bacteria

Bacteria invade bones

SCAVENGER STAGE

OPPORTUNISTIC STAGE

SULFOPHILIC STAGE

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Pigmented blue The mandarinfish (Synchiropus splendidus), found in shallow inshore reefs of the Western Pacific, is one of only two known vertebrate species whose blue colour comes from a pigment, rather than structural scattering of light. The striking blue coloration is used as a warning to predators that it is protected by a powerfully unpleasant-smelling toxic mucus secreted through the smooth, scaleless skin.

blue under water Vivid colours of fish on a coral reef help to signal species identity in this

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crowded community. Blue and yellow are the most common: they contrast well and transmit far under water, while red is effective in shallower depths. Much of this colour comes from pigments that absorb some wavelengths of light and reflect others. But some – notably blue – is structural. This happens when objects, such as microscopic crystals in a fish’s skin, bend wavelengths to different degrees – in the way raindrops produce a rainbow.

PIGMENTARY AND STRUCTURAL BLUES

Incoming light with various wavelengths

Black, brown, yellow, and red pigments are produced in a fish’s skin by cells called chromatophores. So far, blue-pigmented Blue pigment chromatophores (or cyanophores) are absorbs all known only in the mandarinfish and wavelengths a close relative. Pigments absorb waveexcept blue lengths of light, except for the colour that we see, which is reflected back. Other skin Crystal splits cells, called iridophores, contain guanine light into crystals. As light passes through the crystals, different the wavelengths bend to varying degrees. wavelengths Shorter blue wavelengths get scattered back and intensified, so the skin appears Longer wavelengths blue. This explains the blue colour are transmitted of other kinds of coral reef fish. through the cell

Blue light is reflected

CYANOPHORE

Shorter blue wavelengths are reflected

IRIDOPHORE

inflatable bodies The related puffer fish, balloon fish, and porcupine fish all share the startling defensive strategy of rapid inflation of the body to a near spherical form in order to deter attacks from larger animals. They also produce potent toxins. However, these defences sometimes come too late – large, quick predators may snap up a fish before it has fully inflated, which can result in the death

GULPING WATER When frightened, puffer fish and porcupine fish transform by rapidly swallowing water into the stomach, which expands like a balloon, filling all available space in the body cavity. Powerful sphincter muscles at either end of the stomach prevent liquid and gas passing into the gut during inflation. When the perceived threat is passed, the water is regurgitated or belched back out of the mouth and the fish deflates. Backbone

Water flow

of both the fish and the predator. The unrelated swell sharks adopt a similar strategy, but they don’t achieve the extreme roundess seen in the others.

Stomach

UNINFLATED FISH

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Backbone

Difficult mouthful The body of the long-spine porcupine fish (Diodon holocanthus) is covered in rows of scales that extend into needle-like spines. In a relaxed fish, the spines lie flat against the body, but when the fish swells, the skin tautens and the spines are pulled erect, increasing the deterrent to predators.

Uninflated fish uses its undulating pectoral fins to propel itself forward

Skin contains collagen fibres, which help the skin to expand as the fish inflates

Body inflates in 1–2 seconds (it takes slightly longer to deflate)

INFLATED FISH

Stomach inflates around the backbone

Blotchy body coloration serves as camouflage against seafloor

Inflated fish struggles to swim

Spines are modified bony scales

Dugong Hunt (1948) In this bark painting of fishermen in northern Australia’s Gulf of Carpentaria, a dugong – a sea mammal especially valued by Aboriginal people – is pulled from the depths. The work is attributed to the Aboriginal artist Jabarrgwa “Kneepad” Wurrabadalumba.

the ocean in art

aboriginal sea stories The art of Aboriginal peoples in Arnhem Land, in Australia’s Northern and rivers. Traditionally, Aboriginal peoples use art (and oral literature) rather than the written word to pass on their knowledge and tell stories. Works may convey practical skills, such as fishing, or legends of cultural or

Barramundi (20th century) Characteristic of western Arnhem Land art, a pair of barramundi are painted on stripped bark in the traditional X-ray style. The skeleton and organs are mapped out inside the outline of the fish.

Dreamtime Spirits and Fish (20th century) The rock art sites in Kakadu National Park are decorated with paintings and drawings dating back to c.26,000 bce, as well as more recent works. As is typical of Aboriginal rock art, many artists have retold stories by painting over older work. This painting of X-ray-style fish with ceremonial figures is one of 600 works at 46 sites by the artist Najombolmi.

Of all the fish featured in Aboriginal art, barramundi reign supreme. For thousands of years, they were painted on rocks, in sites that are now protected by the Kakadu National Park. Today, the fish is widely reproduced on paper and in bark paintings – an artform that has become widespread in the past 70 years. The bark is stripped from gum trees, then heated and flattened to create a surface for natural pigments. In western Arnhem Land, subjects are depicted in X-ray style (see left). In the east, sea creatures and fishermen are rendered with intricate cross-hatching, known as raark, using reeds or human hair like a

brush to create fine lines. In the northeast, the bark paintings of the Yolŋu people tell tales of seafaring ancestors and legendary sea creatures, and impart centuries of knowledge as the caretakers of the coast. After a barramundi fishing party illegally encroached on a sacred site in 1996, Yolŋu artists in Yirrkala produced a set of paintings known as the Saltwater Barks, to explain their ancient traditions and assert ancestral rights. In 2008, the High Court of Australia confirmed that the area’s Aboriginal owners have exclusive access rights to tidal waters along 80 per cent of the Northern Territory coastline.

By painting ... we are telling you a story ... We use our knowledge to paint from the ancient homelands to the bottom of the ocean. YOLŊU ELDER, SALTWATER: YIRRKALA PAINTINGS OF THE SEA COUNTRY, 1999

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spiritual significance, often using symbols passed down through millennia.

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Territory, reflects their ancient connection with animals in coastal waters

Holding fire The stinging cells (nematocysts) on anemone tentacles are usually triggered by contact with another animal. To avoid being stung, the maroon clownfish (Premnas biaculeatus) secretes a body covering of mucus, to which the anemone does not react.

SECRETING MUCUS The mucus secreted by various fish organs serves many purposes, not least acting as a barrier to pathogens. Mucus contains a cocktail of carbohydrates and proteins, which varies according to the organ and species. Some evidence suggests that clownfish skin mucus appears to lack the proteins that anemones associate with potential threats or meals, and so contact with the fish does not trigger a stinging response.

Cell nucleus

Basal lamina supports cells

MUCUS CELLS IN SKIN

Secreted mucus

Goblet cell produces and secretes mucus

Proteins are produced, modified, and processed for secretion in a series of sacs

mutual protection most notably clownfish. The fish gain protection from predators for themselves and their eggs among the anemones’ stinging tentacles. The anemones benefit because the fish chase away anemone-eaters, drop nutrients from the clownfish droppings boost the growth of algae (zooxanthellae), which live in even closer association inside the anemone, using light energy to make food.

Larvae hatch a week after the eggs are fertilized by the male

Safe nursery Clownfish embryos develop from eggs laid close to anemones, and the young fish are resistant to anemone stings from the moment of hatching. All clownfish begin life as males. The oldest and largest adults switch sex to become females.

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food, and clear the anemones’ tentacles of waste and debris. In addition,

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Several fish species live in mutually beneficial relationships with anemones,

sex changer

Mostly yellow individuals are thought to be females

Many fish change sex during their lifetime, which means that an individual can breed as both a male and a female at different stages of its life. These fish are called sequential (or non-

The wide gape is a threat posture typical of moray eels

simultaneous) hermaphrodites. Most of these sex changers, including several species of wrasse, switch from females to males (protogyny). However, some species switch the other way (protandry), including the common clownfish and, according

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to some experts, the ribbon moray (Rhinomuraena quaesita).

Watching and waiting All morays spend long periods hidden in crevices with the head protruding. Relatively large eyes, expanded nostrils, and sensitive tentacles help the ribbon moray sense prey, which it seizes with its two sets of jaws – one in the mouth, another in the throat. The ribbon moray is sometimes known as the leaf-nosed moray for its distinctive snout.

The female stage A major advantage of protandry, in which a male increases in size and becomes female, is that the larger females have greater bodily resources to invest in egg production, which requires a great deal of energy.

Bright blue body coloration of male

SIZE AND COLOUR VARIATIONS Ribbon morays were once regarded as several species, because of their striking colour variation. However, some experts think that they may develop from small black juveniles into blue adult males and then into large yellow females.

Nostrils flare into delicate, trumpetshaped structures

Can grow up to 130 cm (51 in) long Typically less than 65 cm (26 in) long Typically 65–95 cm (26–37 in) long

JUVENILE

ADULT MALE

ADULT FEMALE

Tip of lower jaw bears three short, fleshy tentacles

The male stage As the ribbon moray matures, the jet black of the juvenile is thought to change to a distinctive, vivid electric-blue colour. Current thinking suggests this may be the male stage of its life cycle.

Bright blue coloration, except on the dorsal fin, snout, and lower jaw, which are yellow Tall dorsal fin gives the body a ribbonlike appearance

Single dorsal fin is deeply notched between the spines

Large eyes provide almost 360° field of vision

Long, tweezerlike jaws; lower jaw projects slightly forwards when fish feeds

Bold patterns and pulses of sound advertise territorial boundaries

Feeding in pairs Chaetodon lineolatus, which feed mainly on coral polyps, tend to be monogamous; pairs work together to defend a feeding territory.

FEEDING ADAPTATIONS The long, narrow jaws of the longnose butterflyfish resemble a pair of bottlenose pliers, making them ideal for feeding in the crevices of the reef, where many other fish cannot reach. Some other butterflyfish, such as bannerfish, have shorter jaws and bristlelike teeth, which are useful for snatching small prey, such as free-floating plankton, from the water, or picking food off the surface of the reef.

Picks plankton from the water

Reaches deep into crevices

LONGNOSE BUTTERFLYFISH

BANNERFISH

Striking colours fade at night to make resting fish less conspicuous

reef feeders The 5,000 or more species of fish that live on coral reefs feed in many different ways. This helps them divide up the available resources and avoid competition. Only about 130 eat coral polyps directly, while many more take tiny invertebrates hidden among the coral rock. Dominant among the polyp-eaters and rock-probers are the butterflyfish. Their tiny protractile mouths, armed with comblike teeth, are perfect for foraging among crevices or rubble, from where they extract their miniature prey.

Dancing colour Butterflyfish are named for their colourful appearance and the way they flutter above the reef in “clouds”. The yellow longnose butterflyfish (Forcipiger flavissimus, opposite) and the smaller copperband butterflyfish (Chelmon rostratus, above) are both found in reefs in the Indian and Pacific oceans.

Spines of elegant unicornfish are fixed in an open position, while those of most other surgeonfish are retractable

Dorsal fin is yellow in Naso elegans and mostly black in the otherwise almost identical N. lituratus

Sharp end

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Like its close relatives, the elegant unicornfish (Naso elegans) possesses at least two forwardpointing spines on either side of the tail. A flick of the tail can inflict serious wounds.

coral reefs

Sharp spines at base of tail project outwards from body

Body coloration brightens with age: young specimens are grey; older individuals have a yellow chest

bladed fish Most fish are covered in scales, which are small, usually bony plates that grow in the skin. While all scales offer some form of protection, they vary greatly in structure and composition. Some groups have evolved modified scales that serve a particular function. Surgeonfish, including unicornfish and tangs, are distinguished by having large scales on the tail, modified into sharp spines, or scalpel-like blades. These usually lie flat, and the fish raises them when disturbed; however, in some species they are fixed in a raised position.

Defensive weapons Like all surgeonfish, the elegant unicornfish (Naso elegans), sometimes called the lipstick tang, uses its spines as a form of defence. It is rarely aggressive towards other fish and is quite confident, perhaps because of its built-in weapons.

Large eyes provide excellent colour vision

Small mouth, with orange “lips”, contains a single row of sharp teeth used to shred seaweed

Small prey species These fish, especially the hidden bottom-dwellers (cryptobenthics), are the some of the smallest and most plentiful and account for almost 60 per cent of fish consumed by larger species. Cryptobenthic larvae remain close to their parents’ reefs, increasing their chances of survival, so the fish supplies are constantly replenished.

URCHIN CLINGFISH Diademichthys lineatus

Skin is smooth and scale-less, but is protected by a layer of mucus

Translucent cryptobenthic fish that is no more than 2.5 cm (1 in) long

GLASS GOBY Coryphopterus hyalinus

Long, tapered body can be 5 cm (2 in) in length

MAGENTA DOTTYBACK Pictichromis porphyrea

Foragers The water column zone of a reef sees slightly larger fish that feed on the smaller bottom-dwellers, coral polyps, plankton, and micro-invertebrates. They also clean the reef and some, for example, the surgeonfish, also consume algae, which helps to ensure sunlight can reach the coral for photosynthesis.

BULLSEYE CARDINALFISH Ostorhinchus fleurieu

Head has distinctive dark stripe on the snout and electric blue lines at the eyes

Male has bright red dorsal fin that it erects during courtship

FLAME ANTHIUS Pseudanthias ignitus

Laterally compressed shape enables fish to swim through narrow gaps in the reefs

COPPERBANDED BUTTERFLYFISH Chelmon rostratus

Visiting predators The largest and most active predators of the reef’s food chain are the visitors that feed voraciously on fish, crustaceans, and plankton, as well as benthic organisms such as algae, echinoderms, molluscs, tunicates, sponges, and hydrozoans. They range in size from the larger sharks and rays, to huge schools of smaller species such as triggerfish and snappers.

ORANGE-LINED TRIGGERFISH Balistapus undulatus

Enlarged scales above the base of pectoral fin, behind the gill, are used to produce sound

Venomous dorsal spines are raised to deter would-be predators

RED LIONFISH Pterois volitans

Snout is long and pointed with large mouth; upper canine teeth are sometimes visible when mouth is closed

SCHOOLMASTER SNAPPER Lutjanus apodus

reef fish Lower jaw carries a pair of venomous canines, used in defence

Coral reefs cover scarcely 0.1 per cent of the world’s oceans, but are home to around one-third of all described species of marine fish. The three-dimensional structure of a reef – as complex as a rainforest on land – has provided a rich variety of opportunities for fish to evolve in a multitude of different ways, helping them to coexist and interact with the other life around them.

STRIPED BLENNY Meiacanthus grammistes

Colour-changing reef dweller Streaked with blue over a pale brown ground, the elongate surgeonfish (Acanthurus mata) is capable of changing the background colour to dark brown. The species inhabits steep slopes and rocky bottoms and is often seen in large schools. This surgeonfish feeds almost entirely on zooplankton, and can live for more than 20 years.

Long, sharp preopercular spine protrudes between cheek and gill cover

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Body can be up to 50 cm (20 in) long

Upper jaw has outer row of strong canines and an inner band of small teeth

BLUEFIN TREVALLY Caranx melampygus

Jaws of adult fish have 26 small close-set teeth at the top and 24 at the bottom

Pectoral fins control swimming movement, stabilizing the laterally compressed body

coral reefs

Sharp, lancelike defensive spines are folded into small horizontal grooves on each side of the tail

SABRE SQUIRRELFISH Sargocentron spiniferum

Fleshy tassels (cirri) may mimic the white polyps that project from a gorgonian coral

cryptic fish

By staying motionless, the pipefish perfects the deception

Coral reefs and shallow seas are visually complex environments, and many species take advantage of the intricate mix of colour and texture to hide from predators and prey. Ghost pipefish are true masters of the art of camouflage and crypsis, with different species specializing in mimicking the appearance and behaviour of diverse reef-dwelling organisms.

Perfect match The red, elongated body and spreading fins of a harlequin ghost pipefish bear a very close resemblance to the branching colony of a gorgonian coral.

Head down A head-standing posture may help a harlequin ghost pipefish blend in with vertical branches of coral. Other species of ghost pipefish adopt a similar behaviour when hiding in seagrass.

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Eyes on side of head rotate in sockets, providing all-round vision even while the fish is motionless

coral reefs

Relatively long, pipettelike snout

Tiny, toothless mouth at the tip of the snout sucks in prey (typically tiny crustaceans)

Colour shift The harlequin ghost pipefish (Solenostomus paradoxus) changes its appearance to be as inconspicuous as possible at each stage of life. The transparent larvae start off in open water, where they live unobtrusively among plankton. On maturity, they live on the reef, where they are surrounded by gorgonian corals and crinoids and adopt strong colours and textures and a ragged outline.

specialized fins About 99 per cent of all bony fish, of which there are around 30,000 species, are classified as ray-finned fish; this makes them the most species-rich class of vertebrates on Earth. All members of this group have fins made up of fine webs of skin supported by bony rays. The adaptability of this basic structure contributes to the group’s success, with size, shape, and function varying to give fish the specialist abilities that set species apart. In triggerfish, the first dorsal fin is small and triangular and contains three thick, spinelike rays. If the fish is relaxed, the spines lie flush with the back, but if it feels threatened, it raises its spines so they are perpendicular to the body.

LOCKING MECHANISM If a triggerfish feels threatened, it raises the spines in its first dorsal fin. The smaller secondary spine then slots into a groove on the back of the larger front spine, locking it in place. The front spine cannot be lowered until the secondary spine has folded back. Front spine is locked in upright position Second spine acts as trigger Both spines fold down together

DORSAL FIN SPINES OF A TRIGGERFISH

Dual-purpose spine When the reef-dwelling clown triggerfish (Balistoides conspicillum) is targeted as prey by larger species, the lockable spine is an important defence mechanism. In addition to making the triggerfish difficult to swallow, it can be used to wedge the fish in a crevice where the predator cannot reach it.

First dorsal fin, containing three spines, is raised in self-defence

Second dorsal fin ripples to provide source of propulsion

Caudal fin used in short bursts of fast swimming, for example when the fish flees a predator

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Anal fins help to propel fish through water Pelvic fins reduced to a pair of stout ventral spikes

Venus in a half-shell (1st century ce) In the central peristyle (courtyard) of the House of Venus Marina, in Pompeii, a dazzling fresco panel of Venus takes centre stage. Rising fully formed from her half-shell, she is carried forward by the wind caught in her red mantle, and is attended by sea nymphs and a dolphin.

the ocean in art

seas of antiquity The sea played a key role in the two ancient civilizations that underpinned Aegean and extended along the Mediterranean coast, until they came under Roman rule in 146 bce. At its peak, the Roman empire controlled all the lands around the Mediterranean, and many beyond. For both civilizations, the

An ocean floor (1st century ce) A floor mosaic from a Roman calderium (hot bath) features African fishermen chasing fish and sea monsters. It was recovered from the House of Menander in Pompeii.

The sea personified (2nd–3rd century ce) In Graeco-Roman mythology, Pontus or Oceanus personified the sea and fathered a panoply of sea gods and sea life. In this detail from a Roman mosaic in Utica, Tunisia, the watery god, with a beard of waves, seaweed hair, and lobster-claw horns, is attended by erotes (winged cupids) riding on the backs of dolphins.

The perfection of classical Greek art survives in statues, sculpted friezes, and mosaics, but rarely in paint. The few frescoes that remain comprise painted tombs in Paestum, southern Italy, dating from the 5th century BCE , and fragments from the much earlier Minoan civilization on the Greek island of Crete. Two in particular honour the sea: in Paestum, a lone diver flexes his body as he swoops down to meet the water; in Crete, dolphins, painted c.1500 BCE and restored in the early 20th century, play across the walls at the palace of Knossos. Further insights into the art of ancient Greece have emerged through Roman art, largely because the expanding empire

(The dolphin) does not dread man, as though a stranger to him, but comes to meet ships, leaps and bounds to and fro... PLINY, HISTORIA NATURALIS, 77–79 CE

became a melting pot for the cultures that preceded it. Looted classical treasures, such as bronze statues and paintings of mythological scenes, were prized and preserved through faithful copies. Hellenistic gods were renamed and their stories replicated in the frescoes and mosaics that adorned the homes and gardens of wealthy Romans. Sea-life mosaics were favoured for bath houses and courtyard pools, especially in the luxury villas of Pompeii, southern Italy. A famous mosaic from the House of the Faun celebrates the coastal bounty of fish, lobsters, eels, and octopuses in a design that was widely used. In coastal colonies in Turkey and North Africa, mosaics featured sea gods and goddesses, such as Poseidon and Amphitrite, and a host of fish-tailed mythical beasts.

Dolphins were popular in mosaics and frescoes as attendants to Aphrodite or playfully circling fishermen and ships. In his Historia Naturalis (77–79 CE), Pliny the Elder contributed to their magic with his tale of a dolphin who befriends a boy and carries him to school every day.

coral reefs

sea was a major source of inspiration in their mythology and art.

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much of Western culture. The city-states of ancient Greece fringed the

Jaws are covered with a mosaic of hardwearing teeth, which are continually replaced throughout life

TEETH AND DIET The jaws and teeth of fish show a huge variety of specialist forms and functions. For example, the teeth of the queen parrotfish (Scarus vetula), which is a herbivore, are completely blunt, with a highly resilient, replaceable surface that is used to scrape the surface of rock and coral without damaging the underlying bone. In contrast, the carnivorous northern red snapper (Lutjanus campechanus), which feeds on small fish and crustaceans, has needle-sharp teeth that are used as weapons for stabbing and snagging its prey.

Blunt, fused teeth

HERBIVORE (QUEEN PARROTFISH)

Sharp, pointed teeth

CARNIVORE (NORTHERN RED SNAPPER)

Excreting sand As the steephead parrotfish (Chlorurus microrhinos) feeds, it gouges particles of reef and rock from the substrate, which it ingests at the same time as its food. The particles pass through the gut undigested and are then excreted as fine white sand.

Robust beak and powerful jaws are typical of excavating parrotfish

substrate for algae, which in turn provide an abundant food resource for other reef-dwellers such as parrotfish. These colourful fish, which Lurid colours are indicative of males, but like most parrotfish this species changes sex from female to male during its lifetime

are members of the wrasse family, have teeth and jaws that have evolved into a beaklike structure. Some species use their teeth to scrape algae from the reef surface, and in others the beak is so tough it can gouge into the reef. These so-called excavating parrotfish supplement their algal diet with animal matter in the form of coral polyps.

Reef resources The ember parrotfish (Scarus rubroviolaceus, far left) and yellow-finned parrotfish (S. flavipectoralis, left) are closely associated with tropical reefs. They feed by scraping algae from the surface of rocks and corals using their beak. As well as providing a vast surface area for feeding, the complex reef structure also provides shelter for the fish.

coral reefs

The sunlit surfaces of rocky and coral reefs make an ideal growing

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reef scrapers

coastal seas Rich in nutrients from ocean upwellings and land run-off, coastal seas have abundant plant and animal life. The shallow, lightdrenched habitat is ideal for photosynthesis, especially for small plants and macroalgae rooted to the seabed.

absorbing light Like all algae, seaweeds make food by photosynthesis, using sunlight’s energy to convert carbon dioxide and water into sugar and other nutrients. All seaweeds use pigments to absorb this energy, while their fronds maximize the surface area for light capture. Different pigments absorb different colour wavelengths present in white sunlight. Green chlorophyll predominates, but some seaweeds have accessory pigments that make them brown or red.

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The green colour of the frond is due to the photosynthetic pigment chlorophyll, which is packed inside microscopic structures called chloroplasts

Selecting the spectrum Green seaweeds, such as sea grapes (Caulerpa lentillifera), lack the accessory pigments of other coloured seaweeds. Their colour is due largely to chlorophyll, the same pigment used by land plants. Chlorophyll absorbs red and blue wavelengths of light – for use in photosynthesis – but reflects green wavelengths.

The frond’s cylindrical midrib has chloroplasts that carry out photosynthesis; it transports the nutrients produced by photosynthesis to other parts of the seaweed

Grapelike ramulus stores sugars and other nutrients that are generated by photosynthesis; each frond consists of a branchlike midrib carrying rows of ramuli

LIGHT AND HABITAT

Fronds are stiffened with white mineral

Red seaweed In addition to chlorophyll, red seaweeds – such as this Corallina – have accessory pigments known as phycobiliproteins, which reflect more red light and absorb more green.

Photosynthetic pigments help seaweeds to thrive in different habitats. Blue and green light penetrate water more deeply than other wavelengths, enabling red seaweeds that absorb these colours to grow better at greater depths. But the quantity of pigment, as well as the type, is important too: some seaweeds of other colours have higher pigment levels to absorb more light in deeper water.

Red light penetrates less than 50 m (165 ft)

Blue light penetrates more than 100 m (330 ft)

Deeper seaweeds have more pigment for absorbing available wavelengths

SEAWEED DEPTH DISTRIBUTION

spotlight species

giant kelp Forming underwater “forests” rising more than 30 m (100 ft) from the seabed, giant kelp (Macrocystis pyrifera) is a type of algae that acquires food by photosynthesis. It is found off the North American Pacific coast from Canada to California, and in temperate regions of all southern-hemisphere oceans.

Pneumatocysts hold the blades upright, enabling kelp to take in sunlight for photosynthesis

Staying afloat Balloonlike pneumatocysts are filled with a mixture of carbon dioxide, oxygen, and nitrogen that giant kelp cells both produce and absorb from surrounding sea water.

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A forest for carbon capture Giant kelp forests, like this one off the coast of California where blacksmith damselfish shelter, absorb vast amounts of carbon dioxide. They act as natural carbon sinks in a similar way to terrestrial forests and lower seawater acidity levels.

Giant kelp anchors itself to the seafloor using holdfasts – rootlike attachment organs that form a tangled mass around rocks, rubble, and debris on the seabed (see p.27) – to prevent it drifting ashore. Rocky coastlines make ideal fastening places. A primary stipe, or main stem, rises towards the surface, sending out branching side stalks with leaflike blades, each with a pneumatocyst, or gas bladder, at its base that keeps it afloat. At the surface, the kelp covers the water in a type of canopy. Unless compromised by warming seas or overgrazed by sea urchins, kelp can live up to seven years. Kelp forests provide a key habitat for many animals. Holdfasts shelter invertebrates, fish and their larvae, and shelter birds and sea otters during storms. Sharks, sea lions, and seals are also attracted to these rich hunting grounds.

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Giant kelp is the largest living seaweed – the term for large algae growing on ocean coastlines. They are supported by water, which enable some seaweeds to grow to enormous lengths. Giant kelp is thought to have the fastest linear growth rate on Earth, and can increase its length by up to 61 cm (2 ft) per day. In clear, nutrientrich waters where the sea temperature is 5–20˚ C (42–68˚ F), it can survive at depths of 53 m (175 ft), but it reproduces only if the water temperature is below 18–20˚ C (65–68˚ F).

underwater meadows Most true plants cannot grow in the ocean. While the sunlit shallows can be thick with seaweeds and other algae, these are solar-powered organisms that lack true leaves, roots, and flowers. However, seagrasses, such as turtle seagrass (Thalassia testudinum), are flowering plants. Rather than merely tolerating the salty ocean environment, they thrive in it: they bloom and set seed below the surface and cover vast areas of the seabed. At a time of global warming, these photosynthesizing green carpets are globally

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important as efficient stores of atmospheric carbon.

Asexual reproduction Turtle seagrass produces horizontal rhizomes that sprout plant clones, helping the species to form extensive swards – much like grasses do on land.

SEXUAL REPRODUCTION In turtle seagrass, genetic diversity comes from cross-fertilization during sexual reproduction. The sexes are separate: each plant produces either male or female flowers. Male flowers release pollen at night in packages of carbohydrate-rich slime. The slime attracts hungry invertebrates, which help disperse the pollen to female flowers. Fertilized flowers form seeds encased in small fruits. The fruits float before settling on the seabed, where each seed completes its germination.

Sticky pollen bundles

Up to five flowers per plant

Single flower per plant

FEMALE

MALE

Roots anchor seedling to seabed

SEEDLING

Seeds sprout while fruit is floating

FRUIT

Tropical seagrass Turtle seagrass – the favourite food of the green turtle (Chelonia mydas) – is a common seagrass of the Caribbean. Neighbouring plants are interconnected clones, but they also reproduce sexually: their seed-packed fruits disperse on the waves and establish new colonies elsewhere.

producing light Many soft-bodied, jellylike animals of the open ocean can produce light: a phenomenon known as bioluminescence. Species as diverse as jellyfish, hydrozoans, and comb jellies turn luminous if the water around them is agitated – perhaps to scare predators or attract tiny planktonic prey. The light, produced by a chemical reaction in organs called photophores, is most striking when emitted in dark, deep water or at night nearer the surface.

Colourless jelly Like many vulnerable jellyfish, the thumb-sized crystal jelly (Aequorea victoria), a hydrozoan from the surface waters of the eastern Pacific Ocean, has a transparent body. This may help to conceal it from predators against the open water. Its light-producing photophores, which are carried around the rim of its swimming bell, produce a momentary green glow.

Rim of the bell contains photophores, but any light produced is only visible in dark conditions

Transparent bell pulsates to propel the crystal jelly through the water

More than 100 tentacles hanging from the rim of the bell carry nematocysts (stinging cells); they immobilize and catch tiny planktonic prey

HOW PHOTOPHORES WORK Bioluminescence typically depends upon a light-producing chemical and an enzyme. When stimulated by a trigger – such as calcium, in the case of the crystal jelly – the enzyme makes the light-producer undergo a chemical change, which releases light. The distinctive green glow of the crystal jelly happens because an additional component – a fluorescent protein – subsequently changes the wavelength of the emitted light from blue to green.

ARRANGEMENT AND FUNCTION OF CRYSTAL JELLY PHOTOPHORES

Lightproducer Photophores around rim

Densely packed photophores glow green and illuminate the rim of the bell

Fluorescent protein

Enzyme

3. Energized protein emits green light

1. Enzyme locks on to light-producer, causing it to emit energy as blue light

Glowing green 2. Fluorescent protein absorbs light energy

Once activated, a cocktail of chemicals in the photophores of a crystal jelly emits green light; each glow lasts for just a few seconds.

alternating generations Animals that are attached to the substrate must get their nourishment close to the seabed. Hydrozoans – relatives of anemones, corals, and jellyfish – have polyps with tentacles

HYDROZOAN SEXUAL LIFE CYCLE The hydrozoan Obelia grows into an upright branching colony of polyps, some of which generate pods that produce medusae. The free-swimming medusae release sperm and eggs into the water. Larvae develop from the fertilized eggs and eventually settle on the seabed, where they form new polyp colonies. The life cycles of other hydrozoans and related animals vary. Some hydrozoans – as well as corals and anemones – do not have a medusa stage, while certain jellyfish species exist only as medusae.

that may rise only a short distance from where they are

Medusa swims in open ocean

growing. But many also produce swimming, jellyfishlike bells, called medusae, as part of their life cycle. Medusae travel far in the water column, where they catch plankton beyond the reach of polyps. By alternating between polyp and medusa generations, food sources are more fully exploited.

Pod releases medusae

Medusa releases eggs and sperm Branching colony

Larva

OBELIA LIFE STAGES

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Two generations Ernst Haeckel’s Kunstformen der Natur (1904) depicts more than a dozen species of hydrozoan – some as anemonelike polyps (bottom) and others as medusae (top). Not all have a life cycle that switches between the two stages: some do not become medusae and, like many other ocean invertebrates, experience open water only as microscopic larvae.

Fertilized egg

coastal seas

Polyps in close-up The polyps of oaten pipes (Tubularia indivisa) – a European hydrozoan that lacks a medusa stage – carry rings of drooping tentacles on stems that extend up to 15 cm (6 in) from their base.

Gonozooids are reproductive capsules that release larvae; the larvae develop directly into new polyp colonies

Tentacles trap microscopic plankton and transfer them to the mouth at the centre

The Miracles of Mazu (18th century) An album of seven ink drawings, now housed in the Rijksmuseum, Amsterdam, Holland, describes the sea journey of a Song dynasty deputation to the Goryeo court in Korea in 1123 CE. The Chinese ships are under the protection of the sea goddess, Mazu. She is shown here in her traditional red robes, hovering on a cloud and carrying an ivory Hu tablet as a symbol of power.

The Story of the Great Flood (c.1870) In this depiction of a Hindu legend, Matsya (one of the 10 avatars of the Hindu God Vishnu) appears as halfhuman, half-fish. Here, he saves Manu (the first man) and the seven sages from the flood.

the ocean in art

asia’s sea deities of the ocean. In most ancient cultures, the sea’s unfathomable depths and unpredictability gave rise to numerous myths and beliefs, in which natural phenomena – such as storms, currents, and fair winds – were attributed

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Thousands of years of art and storytelling reflect humans’ longstanding awe

to the whims and protective powers of sea gods and goddesses. goddess Mazu. Her story varies with the telling, but she was born Lin Moniang in 960 ce in a Chinese coastal town, where she was renowned for her swimming skills. She gained mystical status after she used trancelike powers to save male members of her family from drowning at sea. In 1281, she was given the official title of Tianfei (“Princess of Heaven”). In the 1400s, Chinese admiral Zheng He had his great deeds carved in tablets of granite in two cities in China. He attributed his seafaring success to Mazu/ Tianfei, describing her as a “divine light” above the mast, calming the crew in rough seas. In reality, this light was probably St Elmo’s fire, a ball of light formed from electricity, which appears on ships at sea in storms. The same goddess is evoked in an 18th-century album of ink drawings (see left), where she is pictured floating above Chinese ships, providing protection. Mazu worship spread to sailors and fishermen beyond China, and lacquered wooden statues, woodcut illustrations, and painted panels of the goddess are found in ADMIRAL ZHENG HE’S DEDICATION TO MAZU/TIANFEI, LIUJIAGANG TEMPLE, 1431 temples dedicated to her across the world.

When we met danger, once we invoked the divine name, her answer to our prayer was like an echo.

coastal seas

In ancient Hindu texts (Vedas), Varuna was the god of the sky, but in later tales he came to symbolize oceans, clouds, and water. In Mysore painting, a classical art form of southern India featuring deities and mythological scenes, Varuna is often pictured riding the makara – a hybrid sea creature resembling a crocodile. Varuna also appears in miniatures that illustrate the 5th-century bce Indian epic Ramayana, rising from the ocean to pacify Rama, an avatar of the god Vishnu. According to the legend, Rama’s wife, Sita, was held in captivity across the ocean, in Lanka. In China, from the 11th century on, the success of perilous sea journeys was often attributed to the benificence of the

Inner whorl of shorter labial tentacles transfers prey to the central mouth

Tube is made from specialized stinging cells and sediment, all bound together by mucus

Tube sanctuary Tube anemones cannot retract their tentacles, but when disturbed they pull themselves into their tube by contracting muscles along the length of their body.

The tentacles disappear as the anemone withdraws its body deep into the tube

Outer whorl of longer marginal tentacles has stingers for catching prey and self-defence

living in a tube Most anemones must make a living attached to a firm surface and can reach no higher than the stretch of their tentacles, but one group has evolved the means not only to live on soft anemones live inside vertical, partially buried, feltlike tubes. Instead of being anchored to the bottom, they can slip upwards

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sediment, but even to move up and down on the seabed. Tube

through the tube or sink deeper inside when danger threatens.

coastal seas

Emerging tentacles A fireworks tube anemone (Pachycerianthus multiplicatus), from European coastal waters, erupts from the confines of its tube to sweep the water with its tentacles for planktonic prey. A mature specimen can have tentacles that span 30 cm (12 in).

ANEMONE ANATOMY All anemones have just one opening to their gut for ingesting food and eliminating waste. The gut is a simple cavity lined with digestive cells. Prey caught and paralysed by the tentacles are transferred to the gut opening, before being digested by enzymes released from the gut lining. The basal disc is attached to a surface in most anemones; in tube anemones, it is free to move up and down.

Mouth Tentacle

Mesoglea (jelly layer)

Body stalk Digestive cells

Epidermis

Basal disc

Gut cavity

CROSS SECTION OF ANEMONE

Touch-sensitive antenna, one of three, aids navigation when the fireworm crawls over a reef

Fleshy projections called palps, one on either side of the antennae, are used to manipulate food

Third, central antenna is shown here curving downwards

Caruncle carries chemical sensors and grows as an extension from the first body segment

Fleshy appendage, or parapodium, carries sensory filaments called cirri and bundles of bristles known as chaetae; each body segment has a pair of parapodia

Green “bombs” are fluid-filled sacs that glow for several seconds after release

Glowing defence The green bomber worm (Swima bombiviridis) – a deepsea annelid – lacks venom but deters predators by releasing luminous “bombs” made from modified gills.

stinging bristles Annelids are segmented worms that include many familiar animals, including intertidal lugworms and land-living earthworms. Their bodies have tiny bristles called chaetae that help with traction when crawling or burrowing. But some marine annelids use their Each tentaclelike sensory filament, or cirrus, may be touch-sensitive

worm is threatened by a predator.

coastal seas

Bundle of bristly chaetae – each chaeta is reinforced with tough chitin and impregnated with chalky minerals to make it brittle, so its tip can break

packed chaetae that break off to deliver a painful sting when the

Stinging worm The predatory golden fireworm (Chloeia flava) is found along Indo-Pacific coastlines. This annelid tracks victims, such as anemones and sponges, using a fleshy organ called a caruncle that “tastes” the water for chemical traces of prey animals. Venomous bristles protect the animal from shorebirds and worm-eating fish.

AGGRESSIVE VENOM Venoms are toxic chemicals that are injected into a victim. Most venomous ocean animals, including fireworms, use their venom defensively, but some deploy it aggressively to catch prey. Cone snails, despite being slow crawlers, successfully hunt fish using a rapid-fire venomous dart, which causes quick paralysis. The dart is a modified radula – a mouthpart used for grazing algae in more conventional snails (see pp.34–35). It is located at the tip of the proboscis, which the snail fires from its mouth.

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chaetae for defence. Aptly named fireworms have brittle, venom-

Siphon “tastes” the presence of fish prey in the water

Proboscis projects from mouth and harpoons fish Mouth expands to engulf paralysed prey

TYPICAL HUNTING STRATEGY OF CONE SNAIL

SCALLOP LIFE CYCLE It is only in the juvenile and adult life cycle stages that scallops can swim independently. These molluscs are hermaphrodites: each individual releases both sperm and eggs into the surrounding water. Fertilized eggs develop into planktonic larvae called veligers – a life stage also seen in other oceanic bivalves and snails. After growing a crawling foot, each veliger settles on seagrass or weed, to which it attaches by sticky threads. Here the scallop grows until it is big enough to escape the attentions of crabs and other bottom-dwelling predators. It then develops into a free-living, sexually mature adult.

Eggs and sperm released into water

Free-swimming juvenile

MATURE ADULT JUVENILE

Young, attached scallop

Attached larva

GAMETES (EGGS AND SPERM) Floating larva

SPAT (FIRST SHELLED STAGE)

PLANKTONIC VELIGER VELIGER WITH FOOT

Unlike other bivalves, scallops have two rows of dozens of eyes that alert them to movement so they can swim away from danger. Each eye has a crystalline lens and a retina for image-processing.

A scallop eye contains a reflective, mirrorlike layer, which improves its light-collecting ability

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Multiple eyes

Escaping danger Scallops, such as this bay scallop (Argopecten irradians) of North America’s Atlantic coast, can use their flapping shell valves in an impressive escape response. Their complex eyes, which give sharp resolution for both peripheral and central vision, may help them to recognize approaching predators.

flapping to swim As their name suggests, bivalve molluscs have a two-part shell. Hinged across the middle, the shell is closed by muscles that span the hinge and contract to pull the halves, called valves, together. Bivalves relax these muscles to open their shells in order to strain particles of food from the water but are otherwise mostly sedentary. Scallops are exceptional: they can swim in open water by rapidly flapping their valves open and shut.

Brown and white mottling helps to disguise the cuttlefish against the sediment of the seabed

Patches of yellow are flashed to startle predators when this colour-changing cuttlefish is disturbed

Buoyancy in miniature The tiny, bottom-living flamboyant cuttlefish (Metasepia pfefferi), of tropical Australia, has a proportionately smaller cuttlebone than mid-water cuttlefish, so it regulates its buoyancy across a narrower range of depths. Its toxic flesh – signalled by warning colours – helps to offset its vulnerability to more agile predators.

Mantle – a sleeve of skin that envelops the cuttlefish – encloses a small cuttlebone in the front half of the body; negative buoyancy helps to keep the animal near the seabed

Knoblike papilla (one of six paired projections) on the upper body break up the outline of the cuttlefish to help with camouflage

The cuttlebone of an elegant cuttlefish (Sepia elegans) extends the length of its body

Each oblong chamber is less than 1 mm long

Cuttlebone When cuttlefish die, their buoyant, gas-filled cuttlebones may wash ashore on beaches. A magnified cross section reveals the stacks of hollow chambers inside.

INTERNAL STRUCTURE

Each arm is equipped with four rows of suckers that handle fish and crustacean prey

Unlike most fish, which stay buoyant in the water by means of

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changing buoyancy an adjustable gas-filled swim bladder (see p.231), some animals an internal shell – their cuttlebone. The cuttlebone’s hollow chambers buoy the animal upwards, which enables it to swim in open water. To descend to the seabed, the cuttlefish floods the chambers with liquid, making the animal negatively buoyant and weighing it down so that it can burrow or “walk” on the bottom.

CEPHALOPOD SHELLS

Pink arms can extend downwards to grip the substrate and be used for “walking” on the seabed

Cephalopods include a range of swimming molluscs: nautiluses, octopuses, ram’s horns, cuttlefish, and squid. The nautilus has an external shell, which is coiled like that of a snail yet chambered like a cuttlebone for buoyancy control. The ram’s horn - a deepwater relative of cuttlefish - uses its internal coiled shell in a similar way. In squid, an internal shell is reduced to a simple, penlike structure, or gladius, for support. Octopuses lack a shell altogether, but they are more flexible as a result.

Coiled, chambered external shell

No shell at all

NAUTILUS

OCTOPUS

Coiled, chambered internal shell

Flat, chambered internal shell

RAM’S HORN

CUTTLEFISH

Reduced internal shell

SQUID

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change their buoyancy to sink or float. Cuttlefish do this with

View of the vortex Taken from the International Space Station in September 2018, this photograph shows the spiralling movement of the vortex around the eye of typhoon Trami in the Pacific.

hurricanes and typhoons Violent tropical storms known as hurricanes (in the Atlantic) and typhoons (in the Pacific) are characterized by spiralling winds of up to 350 kph (220 mph), often accompanied by heavy rainfall. They occur when the temperature in the upper 45 m (150 ft) of the ocean exceeds 27°C (80°F). Water temperature reaches this

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level regularly in the equatorial ocean regions, especially in the Pacific, western Atlantic, and Indian oceans in late summer and autumn. Global warming is increasing the duration, frequency, and intensity of such storms. Hurricanes and typhoons can

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cause serious damage in coastal areas but abate as they move over land and lose contact with the forces that drive them.

INSIDE A HURRICANE An increase in surface temperature causes vast amounts of water vapour to evaporate from the sea surface, which creates huge convection towers up to 15 km (10 miles) high. Low pressure at the surface pulls in more air, creating cloud systems and spiralling thunderstorms. Coriolis force (an effect of Earth’s rotation) causes the winds to spin, and as the storm grows it becomes self-sustaining. Water vapour rises from the surface

Spiralling high winds

Air rises to form bands of dense cloud Air drawn in by low pressure

In the centre, the eye, winds are lighter but the sea surface rises

Each non-retractable arm has suckers along its length for gripping prey

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The fins are pulled against the body during jet propulsion, to give the body a more hydrodynamic shape

Each retractable tentacle carries suckers on its spatula-shaped tip

jet propulsion

A rippling fin runs along each side of the squid’s mantle

Molluscs such as snails and slugs creep slowly on a muscular foot, but some molluscs are able to swim in mid-water. Cephalopods, including squid and octopuses, are the fastest of all mollusc swimmers. They adopt torpedo-shapes to cut through water and can generate significant thrust, notably by shooting a jet of water from a siphon, which propels them with sudden bursts of speed.

Fin power The fins undulate to push against the water. They create most of the thrust for slower, routine swimming, when jet propulsion is not required.

Arms and tentacles point forwards in a tight bunch, allowing the squid to slice through water more easily during jet propulsion

SQUID DURING JET PROPULSION

Extended fins along the side of the body give better control of movements during slow swimming

SQUID DURING SLOW SWIMMING

CREATING THE JET All molluscs have a skinlike mantle – a structure that produces a shell in snails but which envelopes the body like a sleeve in cephalopods. Muscles in the mantle wall dilate the underlying cavity, which swells with water, then constrict to eject a water jet out of a movable siphon. By directing the siphon – and the jet’s thrust – forwards or backwards, the squid can control the direction in which it moves.

Muscles dilate mantle cavity

Water enters cavity through opening beneath mantle

Muscles constrict mantle cavity Closed siphon

Squid moves in opposite direction to thrust from jet

Water jet squirts out of open siphon, creating thrust

MUSCULAR ACTION OF SQUID MANTLE IN JET PROPULSION

Speedy predator Jet propulsion helps the European squid (Loligo vulgaris) to cover long distances quickly. It is reserved for escaping predators and catching fast-moving prey: the eight arms and two retractable tentacles are used to grab fish and crustaceans. But jet propulsion does not allow the fine control needed for turning and other manoeuvres, when the squid relies on using its fins instead.

nudibranchs These colourful molluscs are found in shallow and deep marine

Collage of colour This transluscent white aeolid Coryphella verrucosa is found in the tidal streams and sheltered parts of the northern Atlantic and Pacific oceans. Eggs are spawned in a distinctive coiled white string, and like all nudibranchs, it loses its shell at the larval stage. This species can grow to a length of 3.5 cm (1 1/3 in).

waters the world over. There are more than 3,000 known species; some crawl on the seabed, while others live in the water column. Nudibranchs are divided into two groups – aeolids and dorids. Both types are hermaphrodites, with individuals having male and female sexual organs, but they cannot self-fertilize.

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Aeolid nudibranchs This group have sense organs (rhinophores) at their heads and breathe using tentaclelike outgrowths called cerata that cover their backs. In some, their bright colours act as camouflage; for others, they warn predators of their toxicity. Several species feed on larger, well-armed prey like jellyfish, ingesting their unfired nematocysts, and storing them in special pouches at the tips of the cerata - so the cerata play a role in defence as well as gaseous exchange.

Red oesophagus, or gullet, visible under translucent skin

Rhinophores, or sense organs, have distinctive white tips

Surfaces of side (oral) tentacles and rhinophores are covered with wartlike bumps

EDMUNDSELLA PEDATA 2 cm (3 ⁄4 in) long

Dorid nudibranchs This group are mostly smooth bodied. They have two rhinophores, or sense organs, at the head and tufts of feather-like gills towards the back of the mantle, which they use for breathing. In some species, these gills can be retracted into a special pouch. Like aeolids, they are grazing carnivores and feed on a variety of animals, including other nudibranchs.

BERGHIA NORVEGICA 3 cm (1 1 ⁄ 5 in) long

FACELINA BOSTONIENSIS 5.5 cm (2 1 ⁄ 5 in) long

Orange-tipped body processes can be up to 2 cm (3 ⁄4 in) long

Mantle is covered with small, rounded projections

LIMACIA CLAVIGERA 2 cm (3 ⁄4 in) long

GONIODORIS CASTANEA 4 cm (1 1 ⁄ 2 in) long

Feathery, branched gills surround the anus

NEMBROTHA KUBARYANA 12 cm (5 in) long

Mantle, or upper body covering, extends into long, fingerlike projections called cerata

Muscular “foot”, or underside, enables slug to cling upsidedown to water surface tension

Underside of body is known as the “foot”

Clusters of medium to large cerata feature along entire body

Cerata contain red-brown, red, or yellow digestive glands

GLAUCUS ATLANTICUS 3 cm (1 1 ⁄ 5 in) long

FJORDIA CHRISKAUGEI 2–3 cm (4 ⁄ 5–1 1 ⁄ 5 in) long

PTERAEOLIDIA IANTHINA Up to 12 cm (5 in) long

Furled edges (parapodia) fold for walking on seabed, and open out for swimming

Thick rhinophores are tipped with yellow knobs

Characteristic dark blue-black markings can be continuous or broken

POLYCERA QUADRILINEATA 4 cm (1 1 ⁄ 2 in) long

CHROMODORIS ELISABETHINA 5 cm (2 in) long

HEXABRANCHUS SANGUINEUS 40 cm (16 in) long

Exoskeleton, like that of the lobster, is hardened by the mineral calcium carbonate

Chelae (claws) have the strength to crack open coconuts for food

Land giant

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The coconut crab (Birgus latro), reaching 4 kg (9 lb) in mass, is the biggest land invertebrate – but it is still only a small fraction of the maximum possible size for an ocean-dwelling American lobster.

heavy bodies For animals, growing big has pros and cons. While a large animal might overcome predators or competitors with brute strength, carrying weight puts strain on the body. Arthropods – jointed-legged animals such as crustaceans – wear their skeleton externally as a suit of armour. A bigger arthropod needs thicker armour, but this extra weight restricts movement and limits the animal’s maximum possible size. It is only in water, where body weight is countered by buoyancy, that crustaceans such as the American lobster can grow into real giants.

BUOYED BY WATER Weight – determined by the force of gravity and measured in Newtons – changes according to the medium in which an object exists (air or water). Mass – or the amount of material, measured in kilograms – is fixed. In the ocean, where gravity’s pull is partly offset by upthrust from the water, a large lobster has enough muscle power to move its limbs and walk on the seabed. But on land, the lobster’s weight is much greater, rendering it practically immobile.

Weight of lobster in air: 9.8 Newtons

Weight of lobster in water: 6 Newtons

Mass of lobster is 1 kg Mass of lobster is still 1 kg

WEIGHT AND MASS OF LOBSTER IN AIR AND WATER

Replaceable armour Native to the northwest Atlantic, the American lobster (Homarus americanus) is the world’s heaviest arthropod: the largest recorded specimen exceeded 20 kg (44 lb), although most of its kind weigh much less. Like all arthropods, it must periodically moult its exoskeleton and build new armour to get bigger. Since the American lobster grows throughout its life, the record-breaker might have been over a century old.

Pincerlike chelae on the first pair of legs are enlarged for defence against predators

Long antennae are packed with tactile receptors for sensing in dark or murky waters

Carapace is part of the exoskeleton that forms a shield covering the head and leg-bearing thorax, which are fused together

Elongated abdomen is divided into six articulated segments, which allows the body to flex

Five pairs of walking legs have multiple joints and are tipped with small chelae

Tail fan acts like a paddle when the abdomen is flexed, propelling the lobster backwards – and away from danger

Cirri are strong enough to support the weight of the feather star; they can move back and forth to help the animal “walk” over the seabed

Arms pointing upwards can better catch food particles drifting down from above

Orifices upwards The mouth at the centre of a feather star faces upwards – not downwards, as in starfish – so it is better positioned to receive food particles collected by the arms. Food passes through a U-shaped gut, with undigested waste emerging from an anus, which is also upward-facing.

Calyx (central body) carries the feather star’s upward-facing mouth and contains a short, coiled gut

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Animals that are nourished by tiny food particles suspended in sea water do better if they can spread their body over a wide area to catch more particles. Feather stars – relatives of starfish – do just that, directing feathery arms into incoming currents to trap

COLLECTING PARTICLES True filter-feeders, such as clams, pump sea water through a sieve-like part of the body, but suspension-feeders, such as feather stars, effectively “comb” the water to find food. Hydraulically operated tube feet along a feather star’s arms flick food into grooves, where microscopic, hairlike structures called cilia sweep it towards the mouth.

plankton and floating fragments of detritus, while they “walk” along the seabed on spindly, limblike cirri. Some feather stars can also sweep their arms up and down to swim in mid-water.

Tube feet flick food into grooves

Cilia in grooves waft particles towards mouth

Pinnules of each arm fan outwards in the water to help trap food

Feathery arms Feather stars have arms that grow in multiples of five. Some species have as many as 200 arms. Each arm is equipped with myriad side branches, called pinnules.

SECTION OF FEATHER STAR ARM

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suspension feeding

Under the Great Wave off Kanagawa (1829–33) The fierce energy of Hokusai’s huge wave, poised above the boats caught in its grasp, has made this work (from Hokusai’s series 36 Views of Mount Fuji) the most recognized of all Japanese prints. Although it was common for prints at the time to feature a variety of colours, here a limited palette was used to powerful effect to emphasize the wave’s dominance.

Fish in poetry (1830s) Realistic in detail and delicately coloured, Utagawa Hiroshige’s Kurodai and Kodai Fish with Bamboo Shoots and Berries is one of 20 prints that were commissioned by a poetry guild to illustrate poems about fish.

the ocean in art

the great wave crashing waves of the Pacific and the complex currents and whirlpools of the Sea of Japan – have sought inspiration in the sea. In the Shinto faith, everything in nature, from the rocky shore to the ocean depths, has its own

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Since early times, artists in Japan – an island nation surrounded by the

life force: it is this energy that is almost tangible in Japanese woodcuts.

These waves are claws, the boat is caught in them, you can feel it. LETTER FROM VINCENT VAN GOGH TO HIS BROTHER THEO, 1888

Traditionally, the woodcuts depicted city scenes, including geisha, courtesans, and Kabuki actors, and erotica. They became known as ukiyo-e, meaning “pictures of the floating world” – a reference to transitory pleasures. However, towards the end of the Edo period there was an increasing interest in the natural world, and woodcut artists responded by creating landscapes and seascapes. They drew on literary traditions, while engaging wholly with the moods and rhythms of the sea. Among the most enduring of these woodcut artists are Hokusai, best known for Under the Great Wave off Kanagawa, and Hiroshige, often described as Japan’s last great ukiyo-e master. Hiroshige’s woodcuts reflect the sea in every guise, from waves crashing on rocks and a tranquil distant shore in The Sea off Satta Peak, Suruga Province (1858) to the treacherous currents of Naruto Whirlpools, Awa Province (1855). After Japan opened up to the West in the 1850s, following centuries of isolation, such prints were avidly sought in Europe and the US and revered by Impressionist and Post-impressionist artists alike.

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Woodblock printing, the method used to create woodcuts, was introduced to Japan from China around 2,000 years ago, but it was not until the Edo period (1603– 1868) that the art form was popularized. While only the wealthy could afford paintings, woodcuts were available to all, being printed in their thousands and costing as little as a bowl of noodles. The prints were a collaboration between an artist, who drew the design on paper, a cutter, who carved the design onto wooden blocks through the paper, and the publisher of the print runs. Early prints were monochrome, but by the mid-18th century colour prints, known as “brocade pictures”, were created using separate blocks for up to 20 colours.

Hard jaws are made up of modified ossicles

Muscular arms bend in multiple directions to enable movement across the uneven seabed

Brittle star mouth

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The tube feet on a brittle star’s arms pass food to tiny jaws flanking the mouth beneath the central disc. The food enters a short stomach; undigested waste passes out through the mouth, since the gut has no separate anus.

walking with arms The thick, reinforced skin of a starfish undermines its flexibility, so the animal must crawl slowly using hundreds of tiny, suckerlike “tube feet” (see pp.220–01). But in brittle stars – relatives of starfish – the skin is more supple, and a complex lattice of muscles allows their arms to move more freely in the horizontal direction. By snaking to and fro, the spiny arms of a brittle star can grip the substrate and

Mucus-covered tube feet select particles of food and bundle them together for passage towards the mouth

push forwards; rather than being involved in locomotion, the suckerless tube feet are free to gather food particles.

BODY SUPPORTS Like other echinoderms (urchins, starfish, feather stars, and sea cucumbers), a brittle star has a body that is supported both by hard skeletal ossicles that reinforce the skin and by a system of canals circulating sea water (a water-vascular system) that transports materials. Muscles running along the length of the arms control the arms’ movements.

Ossicles are hard plates in the skin

Longitudinal muscles contract to bend the arm

Water-filled channels move the tube feet

CROSS SECTION OF BRITTLE STAR ARM

Brittle arms A European common brittle star (Ophiothrix fragilis) uses its sinuous arms to walk over the seabed while the animal grazes on detritus and microbes. As the brittle star’s name suggests, the arms break easily, although they can regenerate after injury.

Arms radiate from centre (typically 8–15 in common sun star)

Tube feet have powerful suckers

Sticky ends

Tube feet emerge from grooves along each arm

Each tube foot on a starfish ends in a disc, which secretes adhesive and de-adhesive chemicals. These allow the starfish to bind temporarily to other surfaces.

tube feet Bunched spines aid grip on seabed

One of the traits that define the group of marine animals known as echinoderms is the possession of multifunctional structures called tube feet. They are the main organs of locomotion in starfish and urchins, they sometimes act as touch-sensitive feelers, and their thin skin serves as a surface for gas exchange. They also particles to the mouth, and in starfish their adhesive strength is used to prise open the shells of prey such as mussels and clams.

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On the move The action of tube feet allows the common sun star (Crossaster papposus) to creep across horizontal, vertical, or overhanging surfaces. Each arm contains sensory structures, such as eyespots, which enable the starfish to tell light from shade.

THE WATER-VASCULAR SYSTEM

Tip of arm contains tiny, light-sensitive eyespots

Tube feet are part of a system that uses water pressure to aid locomotion, feeding, and respiration in echinoderms. In starfish, water enters (and leaves) the system via a pore on the top of the body. It then circulates to the ring canal and into the radial canals, which extend along each arm. From there the water can pass into the tube feet, each of which comprises a bulbous sac (ampulla) and a stretchy foot (podium). Contraction of the ampulla forces water into the foot, making it extend.

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play a major role in the feeding process, helping to pass tiny

Tube feet Radial canal Central disc Ring canal Arm

OVERHEAD VIEW Body wall Ampulla Foot (podium)

ARM CROSS SECTION

Number of arms Most starfish species have five arms, but some have 10, 20, or even 50. The underside of each arm is covered in thousands of tiny tube feet, which enable the animal to “walk” over rocks, “climb” seaweed, and grab its prey. Each arm contains a full set of the starfish’s body systems, so if the animal loses a limb it can survive without it. A starfish can also regenerate a lost arm.

Short projections radiate from cushionlike central disc

CUSHION STARFISH Cushion star Ceramaster granularis

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Size The diameter of a starfish can range from a few millimetres to 1 m (3 ft). The size of the central disc can also vary. Some, as in the Pacific blood star (Henricia leviuscula), are very small relative to the arm length; others are very large. The largest known species – the sunflower sea star (Pycnopodia helianthoides) – can weigh 5 kg (11 lb) and live for 35 years.

Starfish can be found in every type of marine environment, from the icy polar oceans to tropical habitats. Some permanently inhabit shallow waters, living in tidal pools and on rocky shores, while others live on kelp beds and all parts of the coral reefs. Species have been observed at depths of 9,000 m (30,000 ft).

FIVE-ARMED STARFISH Cuming’s sea star Neoferdina cumingi

Central disc is less than one-fifth of the total diameter

Arm is edged with paddlelike spines

0.5–1 CM (1 ⁄ 5–1 ⁄ 3 IN ) Paddle-spined sea star Allostichaster palmula

Habitat and depth

Upper body is covered in small “bony” plates

Smooth upper surface covered with layer of mucus

COASTAL TO 100 M (330 FT) Leather star Dermasterias imbricata

Long, thin arms can be 12–15 cm (5–6 in) long

6– TO 16–ARMED STARFISH Nine-armed sea star Luidia senegalensis

Stubby arms are covered with brightly coloured spines

UP TO 30 CM (1 FT) Panamic cushion star Pentaceraster cumingi

8–12 CM (31 ⁄4–5 IN) Pacific blood star Henricia leviuscula

Colour is derived mainly from the blue skin pigment linckiacyanin

SURFACE T0 70 M (230 FT) Blue linckia Linckia laevigata

Entire surface is covered with small spines called pseudopaxillae

100–1,000 M (330–3,300 FT) Common sunstar Crossaster papposus

Venomous thornlike spines cover entire upper surface

starfish A group of more than 2,000 species of mostly predatory marine invertebrates, starfish (or sea stars) are echinoderms, closely related to sea cucumbers and sea urchins. Found in all the world’s oceans, they are recognized for their – usually five-point – radial symmetry. They have no brain or blood. Instead a water-vascular system moves sea water through their bodies, delivering the key nutrients needed for their organs to function.

16– TO 25– ARMED STARFISH Crown-of-thorns starfish Acanthaster planci

Underside of body has more than 15,000 tube feet with suction pads

Jewel of the sea The honeycomb cushion star (Pentaceraster alveolatus) is found in the intertidal regions and reef platforms of the Indo-Pacific at depths of 1–60 m (3–200 ft). Up to 40 cm (16 in) across, this starfish lives singly and in groups close to seagrass beds and a supply of microalgae.

Light-sensitive cells at the end of each arm allows animal to navigate, hunt for food, and hide from predators

UP TO 1 M (3 FT) Sunflower sea star Pycnopodia helianthoides

Cushionlike central disc and arms

Sieve plate (madreporite) where water enters water-vascular system

MORE THAN 1,000 M (3,300 FT) Deepsea star Porcellanaster ceruleus

Rows of prominent spines along centre and sides of each arm

Five-rayed symmetry Most echinoderms have five axes or arms radiating from the centre. On this collector urchin (Tripneustes gratilla), these are seen as five double rows of tube feet (see p.221), interspersed with bands of mostly orange spines.

Spines and tube feet are arranged in alternate bands radiating from the mouth

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Tube feet can extend well beyond the body

spiny skin Echinoderms are a large and highly diverse group of invertebrates found only in the sea. Their name means spiny skin, with the spiniest in the group being the sea urchins. The bodies of sea urchins are covered in long, mobile spines, which can rotate at the base and are used for manoeuvring and to repel predators or encrusting animals. The spines vary according to the species, ranging from fine and bristly to stout and pencil-like.

Hole at top is exit point for digestive and reproductive tracts and the watervascular system (see p.221)

Pore was once the emergence point for a tube foot

Urchin test A sea urchin’s body is supported by a shell-like skeleton called a test. When the urchin is alive, the test is covered in a thin layer of soft tissue, spines are attached to rounded protuberances (tubercles) via ball-and-socket joints, and tube feet extend from the tiny holes (pores). When the urchin dies, the spines fall off and the tube feet and tissue decay, leaving only the test.

Tubercle was once the attachment point for a spine

CLEANING AND STINGING Between the spines covering a sea urchin’s body are tiny, claw-shaped appendages mounted on a flexible stalk. Each appendage (pedicellaria) consists of three movable jaws (valves). Some are used as pincers, to pick debris or algae from the urchin’s body, while others are connected to venom glands, enabling the urchin to deliver a stinging nip.

Spine with ball-and-socket joint at base

Tube foot with sucker

Jaw (valve)

Venom gland

Stalk Non-venomous pedicellaria

VENOMOUS PEDICELLARIA

Spines can swivel and be raised or lowered, useful for wedging the urchin into a crevice or lifting it slightly off the seabed

spotlight species

scalloped hammerhead shark All nine species of hammerheads are instantly recognizable by their wide, flattened heads, known as cephalofoils. Despite its appearance and size, the scalloped hammerhead (Sphyrna lewini) is generally not aggressive to

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humans, but our activity has put the iconic animal on the endangered list. Also known as the kidney-headed shark, the scalloped hammerhead is named for the notched front edge of its head. Its eyes and nostrils are positioned on each end of the “hammer”, giving it better binocular vision and a heightened sense of smell. The cephalofoil may also provide a larger surface area for the shark’s sensory cells, or ampullae of Lorenzini, which enable the animal to sense electrical fields given off by its prey. Scalloped hammerheads have relatively small mouths so live on a diet of fish and invertebrates they can swallow whole. They have been observed using one side of the cephalofoil to pin down a stingray before eating it. Adult scalloped hammerheads grow to around 3.6–4 m (12–13 ft) long. They are found in most temperate and tropical

Front teeth are small and serrated; larger, flatter back teeth are used to grind up shellfish

Whole-food diet Scalloped hammerheads have small mouths in comparison to other sharks so eat prey such as sardines, mackerel, squid, and octopus, avoiding anything larger than stingrays – a favourite.

oceans, usually at depths of 25–275 m (80–900 ft). They often swim alone or in pairs, but periodically huge numbers of adults form schools near underwater sea mounts or off island coasts. Mature animals give birth to large litters of live young (anything from 12 to 41 pups) in coastal waters, but many are eaten by other sharks. Fishing and the shark-fin trade have also taken their toll on juvenile and adult animals. Shark super school Scalloped hammerheads gather in their hundreds to form huge schools. Theories as to why they do this vary from migration to aggression and sexual displays, but it makes them highly vulnerable to targeted fishing.

Eye at each end of cephalofoil gives shark 360-degree field of vision

Taking to the air

Wings hit the surface and make slapping sounds, which travel long distances underwater

Large groups of mobula rays sometimes perform spectacular breaching displays, leaping high into the air. This behaviour is thought to be a form of communication.

Cephalic lobes (paddlelike structures in front of mouth) are curled tight when ray leaps

flying under water Skates and rays, which are very similar-looking cartilaginous fish, have evolved a unique form and swimming style, using their flattened body and ripple their fins to generate propulsion over the seabed. However, the closely related mobula and manta rays, both of which venture higher

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and greatly enlarged pectoral fins. Many species are bottom-dwellers

in the water column to filter-feed, beat their fins up and down – a mode

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of swimming that resembles the flight of birds and bats. Perpetual motion Mobula rays swim continually to maintain a flow of water over their gills. They travel widely, often swimming together in large groups as here, off the coast of Baja California, Mexico. The smaller mobulas are particularly gregarious, frequently gathering in schools of thousands.

FEEDING ON THE WING When feeding, mobula and manta rays swim slowly, using the motion to generate a feeding current. They are filter-feeders, with a mouth that opens to the front, rather than beneath as in other rays. A pair of cephalic

lobes unfurls to funnel sea water and plankton into the mouth. Inside, the feeding current runs over the gill rakers, causing the plankton to ricochet off the filter and flow on to the throat, while the water exits via the gills. Feeding current

Cephalic lobes guide water into mouth

Food collects at back of mouth Gill rakers

FEEDING MOBULA/MANTA RAY

FILTRATION SYSTEM

Water flows out of gills

When hunting, barracudas often swim in schools and head straight towards their prey, relying on short bursts of speed

Careful adjustment Chevron barracudas (Sphyraena putnamae) are fast-swimming predators. They have a large swim bladder, which regulates their buoyancy and saves energy. Adjusting the volume of gas in the swim bladder to compensate for pressure changes when rising or descending can slow the fish down. As a result, barracudas generally make only short vertical movements.

Torpedo-shaped, streamlined body is packed with muscle, making barracudas swift and powerful swimmers

swim bladders As every scuba diver knows, maintaining a steady position in the water can be hard work. For most bony fish living in open water, the energy-saving solution is a gas-filled swim bladder, careful hang effortlessly at a certain depth in the water, without floating upwards or sinking. Bottom-dwelling fish often lack a swim

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control of which gives the fish neutral buoyancy and an ability to

bladder, and the feature is absent from sharks and rays, which rely low-density oil, called squalene, which increases their buoyancy.

ADJUSTING BUOYANCY The swim bladder is a thin-walled sac, which can expand and contract depending on how much gas (mostly oxygen) is inside. When a fish swims upwards, the water pressure drops, which makes the gas in its swim bladder expand. To stop the fish bobbing to the surface, gas is removed from the bladder. The reverse happens when the fish swims downwards: increased pressure means gas is added to prevent sinking. Blood flows to swim bladder through arteries (red) and leaves through veins (blue)

Most of the wall is gas proof; gas permeates only the thinnest areas

Oval window removes gas to reduce buoyancy

Gas gland adds gas to increase buoyancy

BONY FISH

SWIM BLADDER

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instead on constant swimming and have a large liver filled with

keeping out of sight Crypsis is the strategy of remaining hidden. One component of it is camouflage – blending against a background, through body coloration, pattern, and texture – but behaviour is also a key factor. In stargazers, the purpose of invisibility is both offensive and defensive; achieving it means remaining partially buried in sediment on the seafloor, where the fish waits for a chance to ambush prey

ATTRACTING PREY Stargazers tempt prey within range using a scrap of flesh, known as a lure, protruding from the mouth. The lure resembles a small, soft-bodied invertebrate, such as a ragworm, and it can be twitched invitingly to gain the attention of potential prey. Bulging eyes watch intently, and when a smaller fish approaches closely enough, the stargazer opens its huge, upward-facing mouth in a few hundredths of a second, creating a surge of inrushing water that the prey is powerless to resist.

that ventures within striking distance.

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Lying in wait The whitemargin stargazer (Uranoscopus sulphureus) lies partially hidden in the sand of the seabed. Patchy colours and granular skin texture blend with the sand, and by shuffling its pectoral fins and tail under the sediment, the stargazer disrupts outlines and shadows that might alert prey to danger. Sometimes only the swivelling eyes protrude.

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Shock treatment Like all stargazers, the Atlantic stargazer (Uranoscopus scaber) has cryptic coloration. It is also one of the few marine species (together with the whitemargin stargazer) capable of bioelectrogenesis – the ability to produce a jolt of electricity to deter predators.

Electric charge is generated by muscles and delivered through contact, usually with the dorsal fin

Jaw is rotated upwards

Ventral surface is paler and has fewer spots Large head, in relation to the body, and a compressed face

SIDE VIEW

Large, upward-facing eyes detect prey in very low light conditions

OVERHEAD VIEW

Uplifting coastline The scenic shores of the Lofoten Islands, an archipelago off the northwestern coast of Norway, provide an example of a coastline that has been uplifted by tectonic activity.

sea-level change Sea level is the average height of the ocean surface relative to land. This has changed throughout Earth’s history in response to climate change and the movement of tectonic plates. Eighty million years ago, as a result of an expansion of mid-ocean ridges (see pp. 264—65) that caused displacement of water upwards, sea level was 250–350 m (820–1,150 ft) higher than today. At the peak of the last Ice Age (about 25,000 years ago), when a huge volume of water was stored on land in polar ice warming melts the ice caps and warmer sea water expands, sea level is once again on the rise — perhaps by as much as 50 cm

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caps, sea level was 120 m (400 ft) lower than it is today. As global

(20 in) by the end of the 21st century.

Relative sea level may rise or fall in areas of tectonic activity that either uplifts the landmass or causes it to sink. Where the landmass rises, the relative sea level drops and the shoreline advances. Conversely, where the landmass sinks, the relative sea level rises and the shoreline retreats. Both processes produce localized changes to the shoreline, but do not have an overall impact on global sea level. Landmass rises Relative lowering of sea level

Shoreline advances

CONTINENTAL PLATE

OCEANIC PLATE

ADVANCING SHORELINE Relative rise of sea level

OCEANIC PLATE

Shoreline retreats

Landmass sinks

CONTINENTAL PLATE

RETREATING SHORELINE

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REGIONAL SHORELINE CHANGES

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Detecting movement The striped eel catfish (Plotosus lineatus) – the only catfish found in coral reefs – has highly developed sensory organs, including the lateral line, which comprises a series of pores and canals along its flanks. Sensory cells in the lateral line detect vibrations (including low-frequency sound waves) and pressure changes, helping the nocturnal fish to navigate dark water and sense the movement of prey it cannot see.

Black-and-white body patterning warns that the fish is venomous

all-over senses Water is an excellent medium for transmitting a wide range of sensory information, including vibrations and electrical signals. Many fish possess well-developed senses, with those of the catfish family being particularly acute. Their large eyes are useful because light transmission is limited in water, and their hearing is enhanced by tiny bones that transmit sound waves picked up by the swim bladder to the inner ear. In addition, catfish have chemical and electrical receptors all over the surface of their body.

CHEMORECEPTOR ORGANS Catfish are equipped with between 250,000 and several million chemoreceptor organs, which are similar to taste buds but located all over the body, in differing degrees of density. These allow the fish to taste anything they come in contact with, enabling them to hunt effectively in the dark. The taste buds do not have to touch potential food in order to taste it. Any soluble chemicals that come from potential food can diffuse through the water to reach the taste buds and stimulate them.

High density of taste buds along leading edge of the fin

Forward position of barbels, with high density of taste buds, increases chance of finding food in front of fish

CATFISH TASTE BUDS

Elongated dorsal fin merges with tail fin, giving eel-like appearance

Lateral line detects vibrations and pressure changes

Nostrils (nares) contain highly sensitive smell receptors in the lining

Barbel is covered in taste receptors

First fin ray on dorsal fin and pectoral fin deliver a sharp sting

Large eye provides excellent vision in clear water

Sensitive body Pressure-sensitive pores all over a sardine’s body enable it to detect the movements of other fish nearby and react instantly, for example by forming a tight group.

Light-scattering scales make it hard for predators to gain a visual fix on a single sardine

migrating in schools Between spring and summer, an explosion of plankton growth occurs in nutrient-rich temperate seas and many fish arrive from warmer areas to feed. Among these are sardines and anchovies, both small fish in the following seasonal currents. During these migrations, these immense schools draw vast numbers of predators, including seabirds, sharks,

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herring family, which migrate in vast schools of millions of individual fish,

dolphins, and whales, into so-called feeding frenzies.

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Safety in numbers When a sardine school (in this case Sardina pilchardus) senses a threat, it forms an even tighter group, with each fish attempting to stay in the centre of the crowd, where it is less likely to be picked out. The swirling mass of bodies shifts and changes in shape in an attempt to confuse predators.

GROUPS OF FISH Fish often gather in small or large groups. A shoal is a relatively casual aggregation of fish, which move in different directions and include individuals of one or more species. A school is a much more organized group, Loose group of individual fish facing in different directions

SHOAL

in which all members move in a coordinated manner. Schooling behaviour almost always has a defensive function, and smaller fish, such as those in the herring family, often rely on swimming in close-knit schools for their survival. Tight group moves as one in a single direction

SCHOOL

spotlight species

great frigatebird Found on tropical islands in the western Atlantic, Pacific, and Indian oceans, the great frigatebird (Fregata minor) soars above the waves for days, sometimes weeks, at a time. It is nicknamed the “pirate bird” due

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to its habit of aggressively stealing food from the beaks of other seabirds. The great frigatebird feeds mainly on flying fish and squid and flies for hours, watching for prey to break the surface, and then seizing it with its long, hooked beak. While it acquires most of its food this way, it is also a kleptoparasite – an animal that steals prey caught by another animal. Frigatebirds attack other seabirds, especially boobies, in mid-air as they return to their nests, harassing them into giving up meals intended for their chicks. This “mugging” of other birds has earned frigatebirds their common name, as their behaviour resembles that of the man-o’war ships, or frigates, used by pirates on ocean raids (and they are sometimes also called man-o’-war birds). At up to 105 cm (41 in) long and weighing 1.5 kg (3 lb 4 oz), but with a wingspan of up to 2.3 m (7 ft 6 in), the great frigatebird has the largest ratio of

wing area to body mass of any living bird. The area of the wing, as well as its long, narrow shape, enables the bird to fly vast distances in search of food, although it usually stays within 160 km (100 miles) of land in order to roost. However, this aerial specialist has a significant weakness – its feathers are not waterproof, as they lack sufficient preen oil to protect them from sea water. A frigatebird never willingly gets wet as, if its plumage becomes waterlogged, it may be unable to take off again. Attracting a mate Like the related cormorants and boobies, frigatebirds have a throat pouch - called a gular sac. A male inflates his huge, bright-red pouch to attract a mate. The females also have gular sacs but never inflate them.

Wing size and shape enable the bird to utilize air currents in flight

Long, deeply forked tail feathers help to steer during flight

Long-distance soaring All birds have air-filled bones to make them lightweight, but a frigatebird skeleton forms a smaller fraction of its body weight than any other bird, making it the nimblest flyer. It can soar for weeks at a time and sleep mid-flight.

Eyes scan the water for prey and the pelican selects a target Steep dive angle increases the chance of making a catch

Body position adjusts above the water, ready for the dive

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Taking the plunge By diving from great heights – up to 20 m (65 ft) – brown pelicans can better counteract the effect of light refraction at the water’s surface, improving their accuracy in catching prey.

Wings start to fold back; the head and neck begin to stretch forwards

plunge diving

Bill opens ready to engulf the fish; the wings are now in an aerodynamic V-shape

Birds that catch fish underwater must overcome the buoyancy of bodies adapted for flying. But by plunging into the water from great heights, diving specialists such as gannets can reach deeper prey before floating back upwards. Brown pelicans do likewise to take advantage of vast shoals in coastal seas – a strategy that sets them apart from freshwater pelicans, which scoop up their catch as they paddle over the surface.

Skin pouch hanging from the bill’s lower mandible expands to accommodate several litres of fish-filled water

KLEPTOPARASITES Because pelicans spend time draining water from their pouch and manipulating their catch before swallowing it, these birds are vulnerable to thieves, or kleptoparasites. In the Caribbean, laughing gulls (Larus atricilla) often land on the head of juvenile pelicans because the young birds are more likely to spill their fish. But in the Gulf of Mexico, Heermann’s gulls (L. heermanni) harass adults that have a bigger catch.

ADULT AND JUVENILE LAUGHING GULL (LARUS ATRICILLA)

Grabbing the catch The brown pelican targets a single fish but usually scoops up several in its pouch – together with a heavy volume of water, which must be drained before the catch can be swallowed.

Coastal pelican The brown pelican (Pelecanus occidentalis) of Central America and the Caribbean fishes along shallow inshore coastal seas. Here, upwellings of nutrientrich water support some of the biggest shoals of anchovies and sardines on the planet. The bird’s chocolate-brown body contrasts with the largely white plumage of its freshwater cousins.

Upper mandible of the pelican’s bill is reinforced with a strong keel, which helps it support the weight of a heavy catch

Long neck enables the pelican to rest its heavy bill against its breast when on the ground or flying Dark brown plumage is waterproofed with an oily coating

Tip of the bill has a sharp, ridged “nail” that can grip slippery fish firmly

Using tools Back on the surface after a dive, an otter places a carefully chosen rock on its front, then bashes a clam against it to crack open the shell and access its meal.

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spotlight species

sea otter densest coat of any animal on Earth, powerful webbed hind feet, a strong, rudderlike tail, and heightened senses of smell and touch that help it to locate prey in murky waters. It is also one of the few mammals to use tools. Found in the north Pacific Ocean, the sea otter is a member of the Mustelidae family, a group that includes weasels and badgers. One of the smallest marine mammals, an adult sea otter has a body length of around 1.2 m (4 ft). Its body is streamlined, highly buoyant, and – apart from its pads and nose – entirely covered in a dense, two-layered coat of fur. Short, insulating underfur contains up to 155,000 hairs per sq cm (1 million per sq in), while an outer layer of longer guard hairs forms a waterproof barrier against cold seas. Grooming helps the sea Hanging on Sea otters often form groups known as “rafts” when resting on the surface. As well as wrapping themselves securely in kelp, some otters prevent themselves from drifting away by holding another animal’s forepaws.

otter to introduce insulating air bubbles into its fur. Unlike seals or sea lions, otters lack a blubber layer so are dependent on their fur to keep warm and dry. A sea otter spends almost all its life at sea. Besides mating and giving birth in water, otters float on their backs on the surface to eat, sleep, and groom. They dive up to 75 m (250 ft) to forage on the seabed, closing their nostrils and ears while underwater. A substantial food supply is crucial – adult sea otters must eat 20–33 per cent of their body weight each day to stay alive. Long whiskers and sensitive forepaws help detect vibrations in low-visibility conditions, allowing these animals to find clams, sea urchins, crabs, and other invertebrates in near-darkness. Sea otters may stash several prey items in pouches of loose skin beneath their forearms, enabling them to carry more food back to the surface.

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Superbly adapted to its coastal habitat, the sea otter (Enhydra lutris) has the

Ears are small and lack external parts (pinnae), but are very sensitive; dugongs rely more on hearing than sight

Stout whiskers sense objects on seabed, even in cloudy water

Grazing pair Dugongs spend most of their time alone or in pairs. Their feeding habits (known as cultivation grazing) look destructive, but their regular visits result in regrowth of some seagrass varieties, which would otherwise be crowded out by tougher, more fibrous plants. Small eyes high on head provide good field of view, although eyesight is relatively poor

ADAPTED FOR GRAZING The skull of a mature dugong is unique and remarkable. No other mammal has such a pronounced downward turn of the lower jaw (mandible) and upper jaw (premaxilla). This shape means the mouth of the dugong opens downwards, allowing the animal to graze from a relaxed, horizontal position.

MALE DUGONG SKULL

Eye socket

Upper jaw

Brain case

Molar tooth socket

Lower jaw

Sirenians are a group of unusual sea mammals that include the Atlantic manatees and the Indo-Pacific dugong (Dugong dugon). Collectively, they are sometimes known as sea cows because of their grazing lifestyle. They are almost wholly herbivorous,

Muscular lips uproot plants from sediment

favouring tender seagrasses and algae. Since they have a lowenergy diet, dugongs take life at a leisurely pace and are restricted to warmer tropical and subtropical waters, where they do not need to burn energy to maintain a constant warm body temperature.

Grazing trail Dugongs eat every part of their food plant, including the roots, so they create meandering trails of bare sediment as they wander through seagrass beds.

Golden trevally take advantage of small invertebrates dislodged by the dugong’s feeding activity

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Wide, fleshy oral disc can be pushed forwards when sensing or manipulating food

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grazing on grass

spotlight species

humpback whale While humpback whales (Megaptera novaeangliae) are remarkable in many ways – their size, intelligence, and the distances they swim each year – these oceanic mammals are particularly well known for their sophisticated

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vocalizations, or “songs”, produced by males during mating season. Humpbacks get their common name because of the way they arch their backs when diving, creating a humped profile. At up to 60 m (200 ft) long, they are not the largest whales in the sea, but they do hold the record for the longest pectoral fins, which can reach up to 5 m (16 ft) – up to a third of their total body length. Mothers and calves have been observed touching fins while swimming, possibly as a sign of reassurance. Male humpbacks vocalize for up to 20 minutes at a time, creating songs that span several octaves and may be heard up to 30 km (20 miles) away. All males in a group sing the same combination of squeaks, groans, howls, and moans, sometimes adding subtle variations but keeping the theme broadly the same. However, studies show that these songs evolve, developing new themes every few years.

GROUP HUNTING Humpbacks often cooperate to hunt, using various sounds and fin slaps to herd or disorient their prey. “Bubble-netting” is unique to humpbacks: the whales use their blowholes to create curtains of air bubbles, corralling prey into a dense mass, before exhaling more bubbles underneath to drive them upwards. They then swim openmouthed up through the centre of the net, capturing mouthfuls of prey.

BUBBLE-NET FEEDING

Humpback whales make one of the furthest migrations of any mammal on Earth. Many undertake annual roundtrips of around 16,100 km (10,000 miles), spending summer in feeding grounds rich in krill and other plankton – their main source of food – before migrating to spend winter in the warmer waters of their breeding sites. Humpbacks were pushed to near-extinction in the 20th century. However, conservation efforts have ensured that most of the recognized populations are no longer endangered. Marks of distinction All humpbacks have dark upper bodies, but white underpart patterns, found on bellies and beneath tail flukes as well as pectoral fins, are unique to individuals. Whales from the southern hemisphere have whiter undersides than northern-hemisphere whales.

Whales dive to bottom of curtain

Whales swim through net with mouths agape

Rising bubbles form cylindrical corral

Whales swim around prey, exhaling bubble curtain

Rich waters Off the coast of California, USA, cool currents from the Arctic combine with offshore winds to bring nutrients to the surface, leading to the growth of phytoplankton, shown here in green.

upwelling and downwelling Vertical currents below the ocean surface bring water up towards the surface (upwelling) or carry water downwards (downwelling). These currents are most common in coastal regions, but can also occur far from land. The quiet central parts of ocean gyres (surface current circulation systems) are areas where deepwater currents converge and downwelling results. Extreme downwelling

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occurs in areas of the Norwegian-Greenland Sea and around Antarctica, where ice-cold dense water sinks and is carried south by bottom currents. When upwelling occurs, the rising current brings nutrients nearer to the surface, supporting plankton

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growth, which in turn attracts a wide variety of ocean life. Major upwelling zones exist off Peru, Namibia, and western Canada.

THE EFFECTS OF CURRENTS AND WINDS Coastal upwelling of water occurs where surface currents are deflected offshore due to the effect of Earth’s rotation combined with that of the prevailing winds. The movement of surface water away from the shore draws water upwards from the ocean depths. In regions where currents near the surface are deflected towards the coast, the waters are forced downwards to produce downwelling.

Wind direction Surface waters move away from coast Wind direction

UPWELLING Surface waters move towards coast

DOWNWELLING

Water forced downwards

Water drawn upwards

spotlight species

atlantic spotted dolphin Inquisitive, acrobatic, playful, and highly sociable marine mammals, Atlantic spotted dolphins (Stenella frontalis) are found in temperate to tropical Atlantic waters from southern Brazil to New England via

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the Gulf of Mexico in the west, and from Angola to Morocco in the east. Although named for their distinctive mottled skin, these dolphins are born spotless and do not acquire any speckling until they are eight to 15 years old; some remain unspotted so are misidentified as slender bottlenose dolphins. Calves are 60–120 cm (2–4 ft) at birth, but adults can be 1.7–2.3 m (5 ft 6 in–7 ft 6 in) long and weigh 110–141 kg (240–310 lb). These dolphins are capable of diving to depths of 60 m (200 ft) and holding their breath for up to ten minutes. Atlantic spotted dolphins are also found in the shallower waters of the continental shelf and come in close to shore to feed near sandbanks or surf the bow waves of recreational boats. Their diet consists mainly of small fish, as well as bottomdwelling invertebrates, squid, and octopus. They use echolocation for navigating and finding food, and pods often cooperate to hunt, encircling prey to

Spots appear first on back and belly as the dolphin grows to maturity

Spot check The degree of spotting, or mottling, varies among adults, but light spots develop on dark skin and dark on light in the same animal, and it often becomes more pronounced with age.

prevent them escaping. They can often be seen feeding alongside bottlenose, striped, and common dolphins, with which they regularly interact. Coastal pods may consist of as few as five to 15 dolphins, but the average is closer to 50. Occasionally, however, groups merge to travel in “super pods” of 200 or more. Highly communicative, Atlantic spotted dolphins use whistles, squeaks, clicks, and buzzes as well as bubbles to “speak” to each other within a group, both at close and at long range. They also use pulsed barks or “screams” to warn off rival pods. Group activity Pods are seen socializing in the clear shallow waters off the coast of the Bahamas. Through socializing, young males form strong, often lifelong, bonds with other males.

Tall dorsal fin has a strong concave curve on its trailing edge

open oceans the

Many organisms live in the challenging environment of the open oceans. Strong currents and a lack of shelter have led both predators and prey to evolve adaptations for greater speed or to camouflage themselves.

Inflated float Some siphonophores – such as the Arctic species Marrus orthocanna – stay buoyant with the aid of a gas-filled sac. By adjusting gas levels in the sac, the animal can control its level in the water.

Bright orange pneumatophore (gas sac) is situated adjacent to the propulsive bells

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dividing labour A group of animals called siphonophores swim or drift in the ocean like true jellyfish, yet they live in colonies like corals. Each colony is made up of individuals, called zooids, that are adapted to perform different tasks. This division of labour improves the overall efficiency of the colony. Some

open oceans

zooids attached to the colony’s stem provide propulsion and function like the pulsating bells of a jellyfish; other zooids, with a specialized feeding role, have mouths and tentacles like the polyps of a coral or anemone.

Mid-water colony Two swimming bells of a deep-ocean, cup-bearing siphonophore (Sulculeolaria biloba) are attached to a soft trailing stem that carries feeding polyps with tentacles for catching planktonic prey. One of the bells has an oil droplet to help maintain buoyancy.

COLONIAL ORGANIZATION The zooids of a siphonophore share nutrients harvested from planktonic prey through a common stem that is differentiated into two regions: one, the nectosome, with pulsating bells; and another, the siphosome, with polyps and tentacles. A gas-filled float, or pneumatophore, may also be present. In some siphonophores, such as the Portuguese man o’ war, the swimming nectosome is absent and the colony floats on the ocean surface by its pneumatophore, drifting as it is blown by the wind.

Pneumatophore

Pulsating bell

Nectosome

Feeding polyp Stem

Siphosome

Reproductive polyp

GENERALIZED SIPHONOPHORE STRUCTURE

Diatoms These are single-celled organisms whose cell walls are made from opaline silica. They are responsible for the production of much of the world’s oxygen, and for removing carbon dioxide from the atmosphere. The silica in the cell walls make them heavier than other single-celled organisms, but adaptations enable them to remain at the water’s surface for photosynthesis. They are also kept in suspension thanks to water turbulence.

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Dinoflagellates These are organisms with two flagella (whiplike tails) that help them move through water in a corkscrew fashion. Most have bodies covered with complex outer cell walls. Some kinds can catch and absorb other plankton. When too many nutrients are available, large blooms may form, which leads to a phenomenon called “red tides”, toxic to both marine life and humans.

Body is composed of two halves that fit together like a tiny box

Curved cells link to form long, spiralling chains 30–300 micrometres (millionths of a metre) long

GUINARDIA STRIATA

TRICERATIUM FAVUS

Bioluminescent species with numerous chloroplasts; cell size can be 30–1,000 micrometres

PYROCYSTIS PSEUDONOCTILUCA

Cells lack hard outer cell walls

GYMNODINIUM

Flat, disc-shaped cell that lives singly or in colonies

PLANKTONIELLA SOL

Tentacle used to sense and capture prey

NOCTILUCA SCINTILLANS

phytoplankton Organisms that drift with ocean currents and make their own food by photosynthesis are known as phytoplankton. They include microscopic algae and cyanobacteria. As phytoplankton are reliant on sunlight for photosynthesis, they are confined to the upper layers of the oceans. They are vital both to the global carbon cycle (they remove carbon dioxide and release oxygen) and to marine food webs, providing food for all forms of marine life from zooplankton through to whales.

Fanned colony A brackish water diatom, Licmophora flabellata is named for the distinctive fanlike formation of the colony of cells. Adjacent cells are linked at the tips of the main axes, but by forming a “chain” they increase their overall surface area. A benthic species often attached to red and brown seaweeds, it is also found in coastal waters.

Colonial ribbon formed when protrusions on the sides and face of the cells link together

Chloroplasts containing the green pigment chlorophyll for absorbing light

Tiny bristles extend from each cell in the colony, helping it stay afloat

Seamlike slit (raphe) between the two halves is hooked in opposite directions at each end

FRAGILARIA

Horns formed by cell walls enable organism to spin as it moves in water

COSCINODISCUS

CHAETOCEROS DEBILIS

PLEUROSIGMA ANGULATUM

Moon shape gives rise to the scientific name of this widely distributed species Fans are formed from many narrow, wedge-shaped cells

CERATIUM HIRUNDINELLA

Individual cells are no more than 0.25 mm long

TRIPOS LUNULA

Egg capsules suspended beneath the raft contain the developing larvae

Floating nursery A floating egg mass of the violet snail (a species of Janthina) – here viewed from below – is carried by the drifting mother until the eggs hatch into swimming larvae. The larvae spend their early lives with other planktonic animals. As it matures, each larva then produces a thread of mucus that is tipped with air bubbles. This buoys the youngster upwards and brings it to the surface, where it lives out the rest of its days as a bubble-rafting adult.

Buoyant snail A violet snail clings tightly to its bubble-raft with its muscular foot, while the rest of the body hangs beneath. The snail’s shell is especially thin and lightweight, which helps to keep it afloat.

Each bubble takes about 10 seconds to make, as the snail envelopes a pocket of air with its muscular foot

The shell is helical in shape, just like the shells of many more typical snail species

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staying afloat The ocean surface, where Sun-fuelled plankton is at its community of surface animals, called the pleuston, has some unlikely floating members. Instead of crawling over the seabed, violet snails drift in the open sea and prey on buoyant hydrozoans. They use their foot to mould mucus-coated bubbles of air that dry to form an inflated raft. This structure, though delicate, can support an adult snail, even when carrying a clutch of eggs.

PREDATORS AND PREY

The floating raft is composed of dozens of air-filled bubbles, each held in place by a thin coating of dried mucus

Many colonial hydrozoans, which are relatives of jellyfish and anemones, drift among the pleuston supported by gas-filled bladders. Among them are the Portuguese man o’war (Physalia physalis) and the by-the-wind sailor (Velella velella), which use stinging tentacles to ensnare planktonic prey. Other members of the pleuston – including violet snails – are predators of both.

Gas bladders

Sail catches the wind

Stinging tentacles

CROSS SECTION OF BY-THE-WIND-SAILOR

open oceans

most abundant, can be a profitable place to feed. The

sustaining life in the dark Beneath volcanic parts of the dark ocean floor, sea water seeping downwards meets hot, molten rock, causing the water to belch back out of fissures, called hydrothermal vents, as boiling streams of concentrated brine. Bacteria use chemicals in the jets of vent water: the only deepsea organisms to do so. This process supports entire communities of animals around the vents, including swarms of shrimps and giant worms. Vent animals are independent of the light-powered food chains at the ocean

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surface and on land, which start with algae and plants.

The thin, transparent carapace enables more infrared radiation from hydrothermal vents to reach the elongated “eyespots” beneath

open oceans

A pair of pinkish “eyespots” under the carapace detects infrared radiation from vents and guides the shrimp to places where it can find food

HYDROTHERMAL VENTS As hot, chemically rich brine from vents meets the cold, deep ocean, minerals such as iron sulphide solidify into chimneys and clouds of black “smoke”. Bacteria on the chimney walls process hydrogen sulphide in the brine and oxygen from the surrounding water to release energy. They use the energy to make sugar and other nutrients from carbon dioxide and water, in a process called chemoautosynthesis.

Sea water seeps down through the seafloor

Geothermal activity heats the sea water, which mixes with sulphides and gases from the surrounding rock

Hydrogen sulphide reacts in nearby bacteria to release energy Iron sulphide forms chimneys or escapes as “smoke” Hot water shoots up through vents in the seafloor

HOW A HYDROTHERMAL VENT SUPPORTS A FOOD CHAIN

Ocean-floor shrimp The mid-Atlantic ridge shrimp (Rimicaris exoculata) grazes on food-making bacteria and organic detritus in the warm water around hydrothermal vents, often more than 3 km (1.8 miles) deep. In places, this species gathers in hordes of up to 2,500 individuals per square metre.

Red gills absorb the gases – hydrogen sulphide, oxygen, and carbon dioxide – needed by bacteria living in the tube worm’s body

Symbiosis Some animals living near hydrothermal vents, such as giant tube worms (Riftia pachyptila), lack digestive systems for consuming food. Instead, they rely on food-making bacteria living inside their bodies to generate all of their nourishment.

Thoracic chamber contains the reddish-brown gills, which are colonized by food-making bacteria after each moult; the bacteria probably supplement food that the shrimp obtains by grazing

At the junction A diver descends into the rift between the American and Eurasian tectonic plates. Iceland’s Silfra Canyon, which is filled with fresh water, is one of the few parts of the mid-ocean ridge that has been explored.

new ocean floor The global mid-ocean ridge system is by far the longest mountain range on Earth, extending for over 80,000 km (50,000 miles) under every ocean worldwide. The ridge is broad and rugged, rising up to 3 km (2 miles) above the abyssal plain (the seafloor between the continental margins and mid-ocean ridge). It consists of a continuous string of active volcanoes, and follows the line of divergent plate boundaries, where tectonic plates move apart. Earthquakes occur frequently along its length. New ocean floor The vast area of the mid-ocean ridge remains almost completely unexplored. Rarely, the crest of the ridge rises above the sea – for

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is formed along the ridge from the upwelling of volcanic material.

example, in Iceland, where volcanic activity is especially intense.

New oceanic crust is formed along the mid-ocean ridge where molten lava (magma) extrudes onto the seafloor, over 2 km (1.2 miles) beneath the ocean surface. Molten magma continually oozes out through fractures in the crust and cools rapidly to form mounds known as pillow lava. Vertical sheets of dark basalt rock (dikes) harden in the fractures and slowly force apart the two sides of newly formed ocean floor. Upper mantle

Volcanic activity Mid-ocean ridge Movement of divergent plate

Tectonic plate

Oceanic crust Movement of divergent plate Rising magma erupts at surface

Mantle

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THE MID-OCEAN RIDGE

Each armoured plate that makes up the body’s exoskeleton can resist the high pressure at great ocean depths

Head capsule is part of the exoskeleton that acts like a helmet and protects the brain

Antennae, each growing up to 20 cm (8 in) long, contain tactile and chemical sensors that help the isopod to navigate in the dim light on the ocean bottom

A robust, curved claw is carried on each of the 14 walking legs to help grip the ocean floor as well as large food items, including carrion

Armoured giant The most familiar of the isopods are their small terrestrial representatives: woodlice. But some supergiant species – such as the western Atlantic giant isopod (Bathynomus giganteus), from below 800 m (2,600 ft) – can grow to 50 cm (20 in) long. Like a seabed armadillo, it has tough segmented armour that protects it from bigger predators.

Compound eyes collect faint sunlight reaching down from the surface, as well as light coming from bioluminescent prey

Seafloor opportunist Food is scarce at the bottom of the ocean, so the scavenging giant isopod may occasionally turn predatory by using its jointed legs to grab a creeping sea cucumber or slow-moving fish.

The largest animals on the planet live in the ocean. The champion of them

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deepwater giants all, the blue whale, weighs as much as 40 African elephants – the biggest buoyancy (see p.212), and although growth is slow in the cold of the greatest ocean depths, some deepwater animals live long enough to become giants of their kind. Here, there are cousins of woodlice that grow as large as miniature dogs, and squid that can achieve the length of a bus.

OVERSIZE SQUID Reaching up to 10 m (33 ft) in length, the colossal squid (Mesonychoteuthis hamiltoni) is the world’s largest invertebrate. Giant squid (Architeuthis) have longer tentacles but smaller bulk. Despite their size, all these predatory behemoths – typically found at depths of more than 500 m (1,600 ft) – are rarely seen alive. Much of what is known about them comes from specimens washed ashore.

STRANDED GIANT SQUID, NEWFOUNDLAND, 1883

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living animals on land. Bodies can grow more when supported by water’s

Web of tendrils A view from beneath the basketlike body of an Arctic gorgon star (Gorgonocephalus arcticus) – here depicted in Résultats des campagnes scientifiques du prince de Monaco (1909) – illustrates its wide catchment area for trapping plankton. Tiny animals, such as crustaceans, are ensnared by the curling arms and passed to the mouth at the centre.

Central disc consists of a large stomach and a mouth (for both eating food and voiding waste) on the underside

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Extended arms are typically held into the water’s current to catch as much plankton as possible

Dichotomous branches Like most starfish, the bushy gorgon star (Gorgonocephalus eucnemis) has a five-point symmetry around its centre. However, unlike starfish, each arm branches dichotomously, repeatedly splitting in two towards the tip.

Arms can form snakelike coils in any direction; the arms of related brittle stars can coil only in a plane parallel to the central disc

Arms coiled tightly around the central disc during daylight are less vulnerable to predators

branching arms The radial arrangement of arms found in starfish and their relatives allows these animals to creep over the seabed, with movement largely restricted to the horizontal plane. But gorgon stars, cousins of brittle stars (see pp.218–19), can also reach upwards into the water column. Their arms branch into a writhing mass of tendrils that is reminiscent of the eponymous Greek monster. The intertwined tendrils are an effective trap for catching small planktonic animals suspended in the water – a source of food beyond the reach of starfish and brittle stars.

Resting by day Gorgon stars, such as this spiny gorgon star (Astrocaneum spinosum), keep their arms retracted during the day. They extend their arms at dusk and feed throughout the night.

Hydrozoa This is a very large group of animals that are seen as distinct from true jellyfish. As well as solitary organisms with a bell-shaped medusa form, the group includes some colonial forms known as siphonophores, which consist of polyps and sometimes attached medusae (missing from the Portuguese man o’ war). Other hydrozoans may have medusa or polyp forms absent from their life cycle; the eight-strand jelly has a polyp stage, but the golf tee jelly does not.

Mouth with eight folded lips leads to short, octagonal stomach

Gas-filled float (pneumatophore) keeps colony afloat

Long, beadlike tentacles capture and immobilise prey; each bead contains stinging cells (nematocysyts)

EIGHT-STRAND JELLY Melicertum octocostatum

Cubozoa Also known as box jellies or sea wasps, cubozoa are named for their box-shaped medusa, and are the most venomous cnidarians. They have muscular pads, or pedalia, at each corner of the bell canopy, with one or more tentacles attached to each one. The attached polyp stage of the life cycle metamorphoses into a medusa, rather than budding to release multiple medusae as in true jellyfish.

PORTUGUESE MAN O’ WAR Physalia physalis

GOLF TEE JELLY Aeginopsis laurentii

Tentacles are covered with millions of nematocysts that release highly venomous darts

Bell is only 2 cm (3 ⁄4 in) in diameter, but the stinging capsules are the most deadly

Sense organs (rhopalia) are clustered at the base of each tentacle

IRUKANDJI JELLY Carukia barnesi

Staurozoa This group, known as stalked jellyfish, includes animals whose life cycle is more similar to that of a coral or anemone than other jellyfish. They have a stalked, trumpetshaped body and do not alternate between polyp and free-swimming medusa. They attach themselves to a substrate such as coral, from which they hang for the rest of their lives.

Circular membrane at bell base reduces aperture increasing force of water jet for propulsion

WINGED BOX JELLY Alatina alata

COMMON BOX JELLY Chironex fleckeri

Each arm, or branch, is equipped with 100–140 tentacles

Funnel-shaped “head” (calyx) is the same length as its stalk (peduncle)

Arms are connected near the tips by a thin membrane

HORNED STALKED JELLYFISH Lucernaria quadricornis

KALEIDOSCOPE STALKED JELLYFISH Haliclystus auricula

THICK-RIMMED STALKED JELLYFISH Haliclystus salpinx

Scyphozoa Also known as true jellyfish, this is a group of about 200 free-swimming marine species. Polyps of these animals may be less obvious, but are often long-lived. They are most conspicuous in their medusa stage – that is, with an umbrella-shaped body – but this may not form the longest part of their life cycle. They move by contracting and relaxing the muscles of their umbrella.

Bell can be 60 cm (2 ft) across, with 3-m- (10- ft-) long tentacles

Colourful jelly that emits light when disturbed

Four lobes (oral arms) hang down from mouth

MAUVE STINGER OR NIGHT LIGHT JELLY Pelagia noctiluca

Short tentacles form a fringe around bell margin

BROWNBANDED MOON JELLY Aurelia limbata

NORTHERN SEA NETTLE JELLY Chrysaora melanaster

Saucer-shaped bell is thick in the centre and thins out towards the edge

These mostly free-swimming, jellylike predatory animals belong to the group of invertebrates known as cnidarians. Most jellyfish and hydrozoans alternate between polyp and medusa (bell- or umbrellashaped) forms. Like other cnidarians, these animals have radial symmetry and lack a heart and a brain, but use an internal cavity to digest prey, which they catch using tentacles armed with stinging cells.

Mane of hairlike stinging tentacles each up to 36 m (120 ft) long entangle the prey

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jellyfish and hydrozoans

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Giant of the oceans The largest true jellyfish species in the world, the lion’s mane jelly (Cyanea capillata) is a continual swimmer that can cover vast distances in strong marine currents. Most are found in the Arctic, north Atlantic and north Pacific oceans, where they live on a diet of zooplankton, fish, Moon jellyfish, and shrimp.

Ram filter-feeding A large whale shark swimming at 1 m (3 ft) per second can filter around 1 million litres (264,000 gallons) of sea water per hour.

Mouth contains vestigial teeth and spongy filter pads with a mesh size of about 1 mm

filter-feeding sharks Filter-feeding is an efficient feeding system that enables some of the largest animals in the ocean, including baleen whales and some sharks (basking, three shark species feed mainly by passive ram filtration, which involves swimming slowly, with an open mouth, through swarms of plankton and small squid and fish. The food is then filtered out of the water. The whale (29–49 ft) long, can also generate suction to feed selectively on larger items.

Migrating to feed Whale sharks travel huge distances between their breeding areas and feeding waters. Here the shark is accompanied by a remora. These fish attach to sharks by suction using their dorsal fin and feed off the sharks’ faeces and ectoparasites.

CROSS-FLOW FILTRATION The filter-feeding system of the whale shark is known as cross-flow filtration. The feeding current flowing from the mouth passes parallel to the filter pads, where water is drawn out sideways over the gills. Food particles become concentrated into a swallowable mass at the back of the throat. This system is less prone to clogging than one in which the flow hits the filter head on, although sharks do sometimes “cough” to backwash material from their filters.

WHALE SHARK’S FILTERFEEDING SYSTEM

Water and food enter mouth

Food-laden water runs across filter, which catches food

Easily swallowable food mass

Water exits via gills

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shark (Rhincodon typus), which is by far the largest living fish at 9–15 m

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megamouth, and whale sharks), to feed on some of the smallest. All

ocean currents Wind is the principal force that drives currents in the ocean surface. It works in conjunction with pressure gradients caused by gigantic mounds of sea water built up in a series of winddriven loops, known as gyres, and by the effect of Earth’s rotation – the Coriolis effect. These currents are hugely powerful. For example, the flow of the North Atlantic Gulf Stream alone is equivalent to the total discharge of the world’s top 20 rivers added together. Equally important is a vast network of slow-moving, deep currents, involving 90 per cent of ocean water. These currents circulate energy, nutrients, salt, and sediments around the world. Surface and deep-

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sea currents act together to moderate Earth’s climate.

THE CORIOLIS EFFECT Like all moving objects that are not rigidly attached to Earth’s surface, ocean currents are affected by Earth’s rotation. This is known as the Coriolis effect (after the French scientist Gaspard-Gustave de Coriolis, who first described it). This effect causes ocean currents in the northern hemisphere to deviate to the right and those in the southern hemisphere to deviate to the left. Because the speed of rotation is faster at the equator than at higher latitudes, the effect is greatest at lower latitudes.

NORTHERN HEMISPHERE Direction of Earth’s rotation

Initial direction of current Deflection resulting from Coriolis effect

Deflection resulting from Coriolis effect

SOUTHERN HEMISPHERE

Initial direction of current

Perpetual ocean Using data from numerous sources, NASA compiled a visualization of Earth’s ocean currents. This segment of the Caribbean and western North Atlantic shows the Gulf Stream, which flows northeastwards from Florida.

spotlight species

white shark An oceanic apex predator, also known as the great white, the white shark (Carcharodon carcharias) can be more than 6 m (20 ft) long and weighs several tons. White sharks were once feared by humans, yet attacks are rare

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and humans pose the greatest threat to this officially vulnerable species. Although increasingly rare, white sharks have one of the widest geographic ranges of any marine animal and can be found in all cold, temperate, and tropical waters. This slow-growing shark takes up to 16 years to reach maturity, and females only give birth every two to three years. Humans’ hunting for sharks’ jaws, fins, and teeth, and attempts to reduce numbers near beaches, have exacted a heavy toll on their population. However, the white shark possesses remarkable characteristics that make it a formidable hunter, increasing its chances of survival. It is partially endothermic, or warmblooded, so able to maintain its brain, swimming muscles, and stomach at a temperature higher than its ocean habitat. This not only keeps the animal highly active but also helps power astonishing bursts of speed of up to 60 kph (37 mph) when hunting. The white shark also has

REPLACEMENT TEETH Adult white sharks may have up to 300 retractable teeth, arranged in up to seven rows, at any one time. Attached to the jaws only by soft tissues, not sockets, the teeth are frequently lost due to pressure exerted when the shark bites its prey. When this happens, a tooth from the row behind moves forwards to replace it. A white shark can go through 20,000 or more teeth in its lifetime.

LOWER JAW WITH ROWS OF TEETH

a streamlined body and excellent colour vision, as well as the largest scentprocessing organs of any shark. Highly sensitive electroreceptors on its head can detect even the slightest of prey-generated electrical fields. In spite of this, the white shark often relies on ambush tactics when hunting. It typically swims slowly beneath potential prey, which are outlined against the ocean’s surface. However, the prey cannot see their predator because the shark’s dark upper body blends in with the murky depths. When attacking from below, a shark makes a near-vertical strike, often leaping 8 m (26 ft) clear of the water. Tools of the trade This shark has narrow bottom teeth to hold its kill and large upper ones to tear flesh. It favours high-calorie prey such as seals or dolphins, but it eats squid, turtles, fish, and other sharks, too.

Front row

Lower jaw

Second row

Soft tissue connecting tooth to jaw

Dorsal fin, working in synchrony with the symmetrically arranged anal fin, acts as a hydrofoil: as it flaps, it provides some lift as well as a little propulsion

Clavus – a thick, wide frill around the rear of the fish – probably forms from extensions of the dorsal and anal fins that replace the tail lost during development

Tailless wonder The truncated shape of a giant ocean sunfish (Mola mola) arises because the vertebrae and fin of the tail are missing – replaced instead with a leathery flap, or clavus. This works like a rudder, while the vertical dorsal and anal fins flap from side to side to move the fish very slowly forwards.

Cleaner wrasse feeds on parasites infesting the skin; the ocean sunfish itself lacks the agility to dislodge parasites easily

Spiny beginnings The protective spiny skin of ocean sunfish fry is reminiscent of pufferfish – their close relatives. Ocean sunfish fry hatch from eggs with a working tail, which shrinks as they develop.

Wide pectoral fins, which stabilize the body, are retained into adulthood

slow giant Plankton are organisms that drift in water because they lack the strength to swim against currents. Most are tiny, but some much larger animals have such weak like plankton. They include the heaviest bony fish: ocean sunfish. Weighing as much as a rhinoceros, they

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powers of propulsion that they may sometimes move

lack any trace of the sweeping tail most other fish use to

FLOATING EGGS Pelagic (open-ocean) fish are adapted to live at different depths, but most produce buoyant eggs that rise to the surface. Here they hatch into fry that spend their infancy feeding on the microscopic, Sunfuelled plankton. Producing many eggs increases the chance that some will survive. A single ocean sunfish may release 300 million eggs – a record among vertebrates.

Oil in eggs gives buoyancy

Ocean sunfish larva Bristlemouth larva

Ocean sunfish lives near the surface Thick, scaleless skin overlies a layer of low-density gelatinous tissue that maintains buoyancy, even though the fish lacks a gasfilled swim bladder

Bristlemouth lives in the deep ocean As larvae mature, deepwater species swim down to adult depths

Depth (m) 1,000 2,000 3,000 4,000

EGG, LARVAL, AND ADULT DEPTHS OF PELAGIC FISH

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generate thrust.

Carta Marina (1539) The largest and most accurate map of Scandinavia of its time was produced by exiled Catholic priest Olaus Magnus, whose mission was to share the history, culture, and natural wonders of the north with the rest of Europe. It was printed from nine carved wooden blocks and shows Nordic lands and seas teeming with life, including the monsters described to Magnus by fishermen and sailors.

New Map of the Whole World (1648) One of the great works of the Dutch Golden Age of cartography, Joan Blaeu’s breakthrough map Nova totius terrarum orbis tabula is part of a huge atlas showing the discovered world fairly accurately, with northwest America and Australasia indicated in incomplete outlines.

the ocean in art

mapping the seas ago, people have used their cognitive spatial skills to map themselves in relation to their environment. By the 15th century’s Age of Exploration, an increasing number of maps from around the world emerged as Europeans

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Since modern humans first carved designs into rocks up to 40,000 years

recorded territories they travelled to in pursuit of trade and colonization.

Inside this broad expanse of fluid Ocean … a conglomeration of monsters may be found. OLAUS MAGNUS, A DESCRIPTION OF THE NORTHERN PEOPLES (VOLUME III), 1555

rendering of northern Europe produced in distant Mediterranean climes. The geography is immediately recognizable, and even the whorls in the ocean may represent known currents and fronts, but what enchants is the detail. The everyday lives of the Scandinavians – driving sleighs, milking reindeer, and spearing seals –are played out in a natural world teeming with real and fantasy beasts. None more so than in the seas, where a dragon wrestles with a giant crayfish, ships anchor mistakenly on tusked whales, and a red sea serpent is described in the map’s key as “a worm 200 feet long wrapping itself around a big ship and destroying it”. A century later, Dutch cartographer Joan Blaeu’s remarkable map of the world (see above) showcases the great copperplate engraving skills of the Dutch Golden Age. It also ref lects the nation’s prowess in seafaring and the artist’s considerable scientific knowledge. The work features the five known planets in personified form with the Sun at their centre, endorsing Copernicus’s controversial heliocentric theory that Earth orbits the Sun.

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Primitive maps carved in stone or wood, or created in 3D reliefs from sand and clay, were superseded over time by woodblock printing, then copperplate printing in the 16th century and lithography in the 19th century. Medieval map-makers based the proportions of countries on their relative wealth and power. However, this changed in the 14th century, when the works of the Greek geographer and astronomer Ptolemy (c.100–c.170 ce) were rediscovered and translated into Latin. His calculations of the size and proportions of Earth changed Western cartography forever, although they later proved to be incorrect. In 1539, Swedish priest Olaus Magnus produced a map of Scandinavia (see left) – an attempt to correct Ptolemy’s vague

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Blue photophores emit light downwards

Light signals The lanternfish Lepidophanes guentheri, a deepsea Atlantic species, has paired light-producing cells (photophores) along its sides and on its head. These lights are used in communication and courtship.

lights in the dark Bioluminescence, a process in which living organisms produce their own light (see pp.192–93), is particularly common in the unlit waters of the deep oceans. Deepwater fish may use bioluminescence for several purposes. For predatory fish, such as some anglerfish, attracting prey with a luminous lure on a chin barbel or suspended on a structure like a fishing rod can be an energy-efficient way to hunt. Other species use light to disguise their outline (see below), confuse predators, or attract a mate.

LIGHT AS CAMOUFLAGE Some fish, such as the hatchetfish (shown here), have light-emitting photophores on their underside. These help to disguise the fish’s silhouette when viewed from below – a camouflage method known as counter-illumination. The fish can control the intensity of the light that it produces to match that of sunlight filtering down from above, making the fish less visible to predators.

Body covered in silvery, reflective scales

SIDE VIEW

Blue-emitting photophores on the underside

VIEW FROM BELOW

Retina is sensitive to red light, which most other deepsea fish cannot detect Photophores in front of and below the eye produce blue light, but a fluorescent protein makes it appear red (see p.193)

Photophore behind eye glows blue

Highly flexible jaw opens 100° when fully extended to engulf prey up to half the fish’s own size

Seeing red Most deepsea bioluminescence produces blue light, which penetrates further in water than other colours. One group of dragonfish, called loosejaws, which includes the smalltooth dragonfish (Pachystomius microdon) shown here, also has red photophores. Since red light is not visible to most other deepsea animals, it may help the loosejaws see prey or predators without being seen themselves.

Slender barbel bears blue photophores and is sensitive to touch

Huge, sail-like dorsal fin, which extends almost the length of the body, is raised for hunting Tail sweeps rapidly from side to side, helping to maximize thrust and minimize drag

Cornering at speed When hunting, the sailfish (Istiophorus platypterus) raises its large dorsal fin, which aids manoeuvrability and provides stability so the fish can improve its aim. It hunts by probing schools of smaller fish with its long, sharp bill, then swiping suddenly sideways, often stunning or maiming several prey at a time.

Trunk is streamlined and muscular, helping sailfish to reach top speeds when swimming

SPECIALIST FINS The dorsal fin of the sailfish is usually retracted, but when the fish hunts it raises its fin as much or as little as necessary to stabilize a manoeuvre, such as herding schools of small fish to make them easier to catch. The crescent-shaped tail generates maximum thrust and reduces drag, allowing great speed over a long distance.

Fin folds into a groove

RETRACTED FIN Erect fin is taller than the body

RAISED FIN

Elongated, bony bill is an extension of the snout

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Billfish, such as sailfish, marlin, and swordfish, benefit from two key weapons: a long, serrated bill and the ability to swim at great speed. Their bodies are highly streamlined and packed with muscle for both rapid acceleration and endurance. The sailfish is one of the fastest fish, with a top speed of about 35 kph (22 mph) per hour in short bursts.

Torpedo-shaped keel directs flow of water over the tail

Long pectoral fins can help to generate lift when extended

Tail keels Small, horny ridges (keels) on the sailfish’s tailstock make swimming more streamlined and provide stability. The tail beats side to side up to eight times a second.

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built for speed

spotlight species

wandering albatross One of the world’s largest flying birds, the wandering albatross (Diomedea exulans) can be 1.3 m (4 ft 3 in) long and weigh as much as 12 kg (26 lb). This species is found mainly in the circumpolar region of the Southern, or Antarctic, ocean and has a lifespan of 50 years or more.

Elaborate courtship The albatross’s display includes wing-spreading, head-waving, bill-rapping, and a distinctive braying call.

The wandering albatross has the longest wingspan – up to 3.5 m (11 ft 6 in) – of any bird. It is a consummate glider that flies vast distances in search of squid and other cephalopods. A bird can cover up to 10,000 km (6,200 miles) in 10 to 20 days. It often soars for several hours without flapping its wings by gliding on thermals and allowing winds to push it along. An albatross spends most of its life at sea; during its first six years, it may never touch land, although it might rest on the ocean occasionally to digest a heavy meal

or when there is not enough wind to fly. It can drink sea water, as it secretes excess salt via a gland above the nasal passage. Sexually mature at around the age of 11, albatrosses mate for life, but they breed only once every two years. The female lays one egg in a nest of mud and grass, usually on subantarctic islands, and the parents take it in turns to sit on the nest. Unfortunately, human fishing equipment kills thousands of these birds each year, placing the survival of all albatross species in jeopardy.

Soaring across the waves Albatrosses can cover 1,000 km (620 miles) per day, and they have been recorded reaching speeds of 108 kph (67 mph), yet they consume only slightly more energy in flight than when sitting on their nests.

Beneficial feeder The recovery of great whale populations, including that of the endangered blue whale (here off the coast of Mexico), may play a key role in averting climate change. Their faeces are rich in iron, which is released from krill during digestion. This boosts the growth of phytoplankton, which in turn absorb and store vast quantities of carbon.

bulk feeding There are two main types of whale: toothed whales and

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baleen whales, which are filter-feeders and have baleen plates instead of teeth. The blue whale (Balaenoptera musculus), the largest animal ever to have lived on Earth, belongs to the family of baleen whales known as rorquals, distinguished by the grooves or pleats on their throat, which expand to accommodate vast volumes of food-laden sea water. When swallowing a dense swarm of krill, a blue whale can engulf 200,000 litres (53,000 gallons) of water and almost half a million food calories.

HOW BALEEN WORKS Baleen whales have hundreds of baleen plates hanging from their upper jaw. These plates are fringed with stiff hairs, which form a “curtain” that prevents food, mainly shrimplike krill, from escaping with sea water as it is squeezed out of the closing mouth. Krill-laden water enters mouth

Tongue draws back and down

MOUTH OPENS

Water expelled through baleen

Mouth opens to almost 90°

Krill trapped by baleen

Tongue pushes up; expels water

MOUTH CLOSES

Ancient activity The Tao-Rusyr caldera off Onekoten Island, Kamchatka, was formed by volcanic activity that occurred in the northwestern sector of the Pacific Ring of Fire over 9,000 years ago.

destruction of the oceans Earth’s outer layers are divided into huge, mobile fragments called plates. The zones where plates collide, called subduction zones, are the world’s largest recycling plants. Here old rocks in Earth’s outermost layer, or crust, are drawn back down into the interior.

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Newer seafloor is produced at the same rate elsewhere, at midocean ridges (see pp.264−65). Subduction zones encircle the Pacific Ocean, consuming the ocean floor at rates of up to 15 cm (6 in) per year. These are regions of great heat and pressure, and

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produce deep-seated earthquakes and volcanic eruptions in a band called the Ring of Fire. When they occur under the ocean, earthquakes and landslides can trigger devastating tsunamis (see pp.76−77).

COLLIDING PLATES Where two tectonic plates collide, such as an oceanic plate and a continental plate, the pressure forces the older one, which has a cooler, denser crust, beneath the younger plate. A deep ocean trench is formed where seafloor sediments are dragged downwards. As the plates grind past one another, enormous frictional strain is generated. The energy is released by periodic violent earthquakes, while the intense heat created begins to melt the rocks, and this molten magma pierces upwards to form a line of volcanic sea mounts, known as an island arc.

Ocean sediments

Ocean trench

Movement of continental plate

Oceanic plate descends beneath continental plate

Volcanic activity where magma reaches surface

Magma forms as descending plate melts

spotlight species

orca One of Earth’s largest living predators, the orca (Orcinus orca) is also one of the fastest marine mammals, reaching speeds of about 55 kph (34 mph). Often called the “killer whale”, at up to 10 m (33 ft) long it is actually the largest member of the dolphin family – and one of the most intelligent.

Wave-washing Working together, several orcas swim underneath an ice floe to create a large wave that will knock the seal off into the water.

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Keeping in touch Pod members communicate with each other via a sophisticated series of high-frequency clicks and whistles, as well as “pulsed calls”, which, to human ears, sound like screams.

floes. Orcas are the only cetaceans that regularly eat other marine mammals – including other dolphins. Sea lions, octopuses, sea otters, rays, turtles, squid, and penguins are part of the orca’s diet, but what individuals eat depends largely on what population type they belong to: “resident” orcas, which form the largest pods (or groups), mostly hunt fish, squid, and octopuses; “transient” orcas feed almost exclusively on marine mammals; while “offshore” orcas mainly hunt fish, especially sharks. Pods range from just a few animals to groups of 50 or more and usually consist of a mature female and her female offspring and relations. Orcas can mate year round, but most matings occur during late spring and summer. Following a gestation period of around 17 months, the female gives birth to a single calf, which is usually born tail-first.

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Found in every ocean, orcas have the widest distribution of any sea mammal on the planet. Striking black-and-white markings make orcas easy to spot, particularly as adult males bear the largest dorsal fin of any cetacean, with some reaching up to 1.8 m (6 ft) high. The orcas’ success is due in part to their range of sophisticated hunting techniques, which are taught to juveniles by adults. These include coordinated attacks on large whales, herding fish before stunning them with powerful tail strikes, and “wave washing” seals off ice

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the

Low temperatures in the polar oceans slow the movement and growth of plants and animals. Yet the water is rich in oxygen and nutrients, enabling marine life to thrive in this extreme environment.

spotlight species

sea butterfly A tiny zooplanktonic sea snail sporting twin translucent winglike appendages, the sea butterfly (Limacina helicina) is critical to the ecology of the Arctic seas. It feeds on zooplankton and phytoplankton, which it traps by casting a net of mucus.

FLYING THROUGH WATER Sea butterflies swim by moving their parapodia, or “wings”, in the same figure-of-eight pattern seen with the wings of flying insects. Both animals generate lift on up- and downstrokes by peeling their wings apart at the start of each downstroke, and rotating each wing slightly during the upstroke.

“WING“ MOVEMENT MADE BY A SEA BUTTERFLY

Path followed by parapodia

Downstroke powers lift

Recovery stroke Powered upstroke

Upstroke powers lift Parapodia formed from modified foot

Body rotates as it moves in water

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Weighty armour Sea butterflies are normally protected by their dense aragonite shells. However, their shells are heavy, and the animals sink rapidly if not actively swimming or hanging from their mucus feeding-webs.

These minute animals have a short, one-year life cycle and, when they die, their shells fall to the seabed. This creates an effective carbon “sink” that keeps tons of carbon dioxide (CO2) out of the atmosphere and helps to slow the rate of global warming. However, oceans absorb more than 25 per cent of the rising CO2 emissions, which raises acidity levels (lowers their pH). Ocean acidification hinders the sea butterflies’ ability to build their protective armour by reducing the speed at which their shells grow and the availability of aragonite. While a damaged or non-existent shell does not necessarily kill sea butterflies, it does leave them vulnerable to predators and disease. The size and health of the sea butterfly population is therefore a key indicator of how much ocean ecosystems are being affected by global warming.

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Sea butterflies are pteropods, or freeswimming marine gastropods, that propel themselves with elegant parapodia (or “wings”) adapted from a modified foot. Their 1–14 mm (1/25 –1/2 in) thick shells are formed from aragonite, a type of calcium carbonate absorbed from sea water. At the bottom of the Arctic food chain, sea butterflies create huge swarms in the upper reaches of open Arctic waters, where they consume plankton – even other sea butterflies. They, in turn, are eaten by whales and seals, which can be prey for polar bears.

Intricate patterns This aerial view of sea-ice off the Icelandic coast shows small segments of sea-ice (right) formed offshore combining to produce larger expanses of ice (left) in the shallower waters near the coast.

sea-ice The water in the ice-cold polar oceans freezes and thaws in an annual cycle. During the winter months of 24-hour darkness, temperatures can drop to to -30°C (-22°F) so that the sea freezes over to form sea-ice. When water freezes, it is less dense than it is as a liquid. Consequently, the ice that is formed floats. Each year,

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this sea-ice covers a remarkable 40 million square km (15 million square miles) of frozen ocean, which is equivalent to the area of Russia, China, and the US combined. In summer, 60–80 per cent melts back into the ocean, with no net effect on sea level. Any ice

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that remains frozen through the summer grows thicker year-onyear and drifts in the ocean currents, but the area of permanent sea-ice is fast diminishing as global climate warms.

HOW THE SEA FREEZES Freezing winds across the ocean surface cause ice crystals to grow in the polar waters. These lock together to form a slushy surface layer, known as grease ice, which hardens and thickens into a continuous sheet. Wind and waves may break the cover into pieces that jostle and bump to form separate platterlike shapes of solid ice called pancake ice. These eventually fuse into larger sheets up to 2 m (7 ft) thick, which continually separate into ice floes and then freeze together again. Near the shore, thick layers of ice that endure for many years may form.

Ice crystals form near surface

Grease ice

Pancake ice

Thick layers of multi-year ice Ice floe

Swimming legs are attached to the abdomen

Large compound eyes capture light and provide almost 360° vision

Stomach is full of phytoplankton (algae)

Feeding legs (setae) on the thorax bear fine bristles for sieving food from the water

Feathery gills are attached to the thorax

Underside of pack ice is often covered with “lawns” of algae on which krill graze

Primary antennae are used for touch and smell

Tips of legs are used for scraping microscopic algae (diatoms) from the underside of pack ice

Seasonal plenty Antarctic krill (Euphausia superba) grow to 5–6 cm (2–2½ in) long on a diet of mostly single-celled algae such as diatoms. They feed by filtering algae from the water using their bristly legs and by raking algae from the underside of pack ice. During winter food shortages, they can reduce body size to limit the chance of starvation.

Marine biomass Krill are among the most numerous animals in the ocean, with some swarms of krill containing more than 10,000 individuals per cubic metre (35 cubic feet). Whales, seals, seabirds, fish, and squid consume up to 300 million tonnes of Antarctic krill a year.

The angle at which Earth tilts as it circles the Sun results in extreme summer, extended daylight hours create a massive boom in the growth and reproduction of marine phytoplankton (mainly single-celled algae) and consequently also in the animals that feed on them. These include small, shrimplike crustaceans known collectively as krill, which constitute one of the most abundant life-forms and food sources on the planet.

Secondary antennae are longer and more whiplike than primary antennae

MARINE FOOD WEB Phytoplankton live on the surface of the ocean, where they can capture the Sun’s energy, which is needed for photosynthesis. As the primary producers, they form the base of the marine food web. In the Antarctic, the phytoplankton are then eaten by krill, which are the primary consumers and hold a critical position in the food web because of the sheer variety of other animals that feed on them. In the Arctic, copepods replace krill as the primary consumers.

SUNLIGHT SEABIRD

ORCA

PLANKTON

PENGUIN

BALEEN WHALE

KRILL

FISH

SEAL

SQUID

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seasonal variation in the amount of light reaching the polar regions. In

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polar swarms

Arctic specialist The sculpins are a family of small fish that are common in the icy seas of high northern latitudes. The antlered sculpin (Enophrys diceraus), native to seas around Alaska and Siberia, shows some of the highest levels of blood antifreeze protein known in any fish.

Eye situated high on head enables fish to scan water above for food and predators

Upturned mouth adapted for grabbing food from below

Fleshy growths may mimic seaweed and aid camouflage

Most of body length is tail, packed with muscle

Cold-water adaptations Antarctic icefish, such as the mackerel icefish (Champsocephalus gunnari), are the only vertebrates that lack haemoglobin. They can survive without it as they live in extremely cold water, which is high in oxygen. To prevent their blood freezing in the icy ocean, they produce antifreeze proteins.

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Since water expands when it turns to ice, freezing can be lethal to living organisms, causing cells to rupture. Sea water remains liquid to about -2°C (28°F), and organisms living in sub-zero conditions have evolved to cope. While mammals and birds burn sugars and fat to keep warm, many fish produce antifreeze proteins that inhibit ice formation.

ANTIFREEZE PROTEINS Many fish living in polar waters produce proteins in their bloodstream that prevent the fish from freezing. These antifreeze proteins (AFPs) bind to the corners of tiny ice crystals in the blood and prevent the crystals linking up. As a result, provided there are enough AFPs in the fish’s body, ice crystals do not grow sufficiently large for the blood to freeze.

AFPs bind to ice crystals Ice crystals cannot link up beyond a certain size

ICE CRYSTALS IN FISH

Crystals free to link up to form solid ice

ICE CRYSTALS IN WATER

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antifreeze in fish

zooplankton Fantastical larva The deepsea-dwelling cusk-eel (Brotulotaenia nielseni) lays eggs that float up to the surface, where they hatch. The planktonic larvae live at shallow depths, only making their way to the bottom as they mature. The larva’s elaborate fin rays and external gut make it resemble a siphonphore colony with its stinging tentacles, possibly to deter would-be predators.

Animals that drift with ocean currents because they cannot swim or are very weak swimmers are known as zooplankton. They include some of the tiniest animals in the oceans, which, together with phytoplankton (see pp.258–59), form the base of marine food webs. For these creatures, the viscosity of water can make forward progress the equivalent of a human moving through syrup, so they depend on the currents for dispersal. Some are the larvae of animals that

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are free-swmming as adults, others live out their lives as plankton.

Meroplankton This group of zooplankton are plankton for part of their lives only, usually the larval stage, and many bear little or no resemblance to their final adult form. They feed on other plankton or may live off the yolk of the egg from which they hatched. As adults they may either move to the benthic (deeper ocean) waters or stay in open water.

Convoluted bands of microscopic beating hairs (cilia) aid propulsion

Tail-like abdomen folds underneath the adult crab during metamorphosis

MEGALOPA STAGE BOX CRAB Calappidae

Holoplankton Animals that remain as plankton for their entire life cycle are known as holoplankton. They live in the open (pelagic) water column, and, like meroplankton, most are transparent. They vary in shape and size and are equipped with a variety of adaptations, from body shape to gas-filled floats, to assist survival.

Transparent mantle contains pigment-containing cells (chromatophores) that form early in development

TORNARIA LARVA Ptychodera flava

Spindly, antennaelike appendages twitch so they appear to jump through water

WONDERPUS OCTOPUS LARVA Wunderpus photogenicus

Fleshy, winglike flaps (parapodia) help sea slug propel body through water

Flat-shelled snail that can be up to 3 cm (1 1 ⁄4 in) long

BRISTLEWORM Tomopteris helgolandica

SEA ANGEL Clione limacina

SEA BUTTERFLY Clio recurva

Dorsal and anal fins resemble a bird’s feather

Large eyes point upwards, enabling fish to see food falling from above

Trailing external gut increases the surface area for absorption from ingested food

Larva has an eye on either side of its head and swims vertically

JUVENILE DEEPSEA HATCHETFISH Argyropelecus olfersii

LEFTEYE FLOUNDER LARVA Engyprosopon xenandrus

Mirrorlike eyes are used by this crustacean to locate small animal prey

Full intestine visible through transparent swimming body of this snail

Surface is covered with cartilaginous tubercles

GLASS SQUID Cranchia scabra

OSTRACOD Gigantocypris muelleri

SEA ELEPHANT Cardiapoda placenta

Chicks huddle together in groups from the age of three months while the adults hunt for food

Contrast in appearance Covered in brown fluffy down for the first year of their lives, king penguin chicks bear little resemblance to their parents – so much so that they were once thought to be a completely different species.

king penguin Atlantic and Indian oceans. There are more than 2.2 million king penguins (Aptenodytes patagonicus) around the world, and the largest concentration is on the island of South Georgia. At up to 1 m (3 ft) tall and weighing up to 16 kg (35 lb), the king penguin is second in size only to its closest relative, the emperor penguin (A. forsteri). Its colonies are usually established with close access to the sea, where nests can be built on flat beaches or in tussock grass free of snow and ice. At 13–16 months, including the adults’ pre-moulting period, king penguins have a much longer breeding cycle than any other penguin. They do not build nests. Females lay one egg between November and April, which they pass to their mates, then they return to the sea to hunt. The Group dynamics King penguins are highly sociable. Even in the largest colonies, where adults stand flipper to flipper, fighting is rare. However, breeding adults tend to remain separate from non-breeding birds.

males carry the eggs (and later, the new chicks) on their feet and cover them with a brood pouch. Males can lose up to 30 per cent of their body weight as they wait for the females to come back. Later, groups of chicks huddle together while both parents go to sea in search of food; feeding sessions are up to 3 months apart, so they too rely on fat reserves to survive. Adults can swim up to 500 km (300 miles) before finding enough fish and squid. There are signs that shifts in the Antarctic Polar Front might increase this distance even further as the penguin’s prey moves in response. A king penguin’s eyes are adapted to extreme differences in light conditions. In sunlight, their pupils constrict to a pin-sized opening, but in low light, for example when diving to depths of 300 m (1,000 ft), they expand by 300 times – the widest alteration of pupil size in any bird.

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These birds are found mainly on the subantarctic islands of the southern

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spotlight species

BLUBBER

Dermis

The blubber of cetaceans and pinnipeds is a thick, relatively firm layer of fatty tissue lying under the skin (made up of the epidermis and dermis). In addition to the adipose (fat) cells, the blubber contains abundant collagen fibres, which stabilize the fat layer, and it is bonded tightly to the underlying muscle by a layer of connective tissue. Blubber thickness ranges from 2 cm (¾ in) in a small seal or a porpoise to about 30 cm (12 in) in large whales.

Epidermis

Blubber

Dispensing with fur The walrus (Odobenus rosmarus) has a thin coat of fur, but by adulthood it often becomes virtually bald, except for a moustache of massive, bristly whiskers. These thick, touch-sensitive hairs are a vital aid to hunting prey, such as clams, in soft sediments.

Connective tissue Muscle

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CETACEAN SKIN AND BLUBBER

insulating layers For mammals living in cold seas, heat loss can be a constant challenge.

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Cetaceans (whales, dolphins, and porpoises) and pinnipeds (seals, sea lions, and walruses) rely on a thick layer of fat under the skin, known as blubber, for their survival. The blubber prevents body heat escaping through the skin and also stores energy, including proteins and fats. The thickness and fat content of blubber can be adjusted seasonally, and the blood supply is restricted during dives to minimize heat loss.

Flexible protection The skin of a male walrus is anything up to 6 cm (2½ in) thick, overlying a layer of blubber at least as thick again. In addition to insulation, this full body padding provides significant protection and serves as a kind of soft armour when fighting.

Scars on skin of males are evidence of “tusking”

Short, sparse hair may be retained on the head, even after body hair has been shed

Nostril linings are the thinnest part of the skin; walruses have a welldeveloped sense of smell in air

spotlight species

southern elephant seal The world’s largest seal, the southern elephant seal (Mirounga leonina), is named for its size and the trunklike inflatable proboscis seen on mature males, or bulls. These animals exhibit the greatest gender-related size and

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weight disparity of all mammals. Found in cold Antarctic and subantarctic waters, elephant seals feed only at sea and can spend up to ten months a year in their search for fish and squid. They typically dive for 20–30 minutes, although they can can remain underwater for up to 2 hours and reach depths of 2,000 m (6,500 ft) or more. To achieve this, they exhale before diving to eliminate gases that could cause sickness. To ensure a constant oxygen supply, they have twice the amount of oxygen-carrying haemoglobin in their red blood cells as land animals of similar sizes and store more oxygen in their muscles. Their heart rate can slow to 5–15 beats a minute, so blood flows only to vital organs. Although elephant seals see poorly in daylight, their vision is adapted to hunting in deep, dark water. Their eyes are highly sensitive to the wavelengths of light (see pages 258–59) given off by bioluminescent lanternfish, a main source of food.

Their extended feeding periods ensure these seals accumulate enough fat, or blubber, to see them through two lengthy periods of time on land: a month-long moult between January and February; and the breeding season, which starts around mid-August. The seals return to the same place on land every year. Bulls can spend weeks, or months, fighting for control of harems of females, then breeding with them. The largest bulls acquire vast harems of 50 females or more.

Coming ashore for breeding A male southern elephant seal hauls himself out on the island of South Georgia, also the site of a vast king penguin breeding colony. More than 50 per cent of the global population of these seals come to breed here.

Size difference Sexual dimorphism – when males and females of a species show marked contrast in appearance – is extreme in these seals. Males can weigh up to 3 tonnes (6,000 lb); females weigh just 600–800 kg (1,300–1,800 lb).

Huge males can be up to 10 times larger than females

Females mate again a few days after their pups are weaned

sensitive whiskers Mammalian hair serves multiple purposes. In seals it provides individually unique patterning, waterproofing, insulation, and

THE WHISKER SENSORY SYSTEM Seal whisker follicles are packed with blood vessels and nerve fibres, which process sensory data and relay information about the physical environment to the brain via the trigeminal nerve. Whisker

vital sensory information. Seals have long, stiff, highly sensitive whiskers (or vibrissae), which grow from hair follicles that detect the slightest vibration and transmit the information

Skin’s epidermis

along sensory nerves to the brain. This enables seals to

Whisker capsule

Sensory nerve endings

navigate in murky water and pick up on prey or predator

Deep whisker nerve

Whisker grows from follicle base

movement, and helps them to assess the size of breathing

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and access holes in the ice.

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Superficial whisker nerve

Adult fur is greasy and virtually waterproof

Summer bask Weddell seals (Leptonychotes weddellii) leave the sea in the short Antarctic summer to give birth, bask, and moult. Unlike the whiskers, which grow throughout the year, the seal’s fur is shed and replaced annually.

Coarse, stiff whiskers enable seal to detect prey up to 180 m (590 ft) away

SEAL WHISKER

Whiskers of pups are thinner and less coarse than those of adults

Downy lanugo provides good insulation before the pup develops blubber

Seal pup The Weddell seal is born with whiskers and is covered in lanugo, a fine, dense fur. After four weeks, the lanugo is replaced by the more waterproof adult coat.

Hind flippers of true seals give propulsion when swimming and cannot support the body on land

Front flippers are used for steering and adjusting speed when swimming; hind flippers provide propulsion

Fantastic forms This immense iceberg was formed in Disko Bay, western Greenland, where the Ilulissat Icefjord flows into the sea. Ten per cent of the ice that fragments from Greenland’s glaciers comes from this glacier.

ice-shelves and icebergs Ice-sheets and glaciers lock up huge volumes of water over the landmasses of the polar regions. In coastal areas of Antarctica and Greenland, ice-sheets and glaciers extend over the sea as vast ice-shelves that can form towering cliffs up to 50 m (160 ft) high.

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Ice-shelves are composed of dense ice that has accumulated over hundreds of years and are often a vivid blue, because all the tiny white air bubbles have been squeezed out. Marine algae frozen into the ice may give parts of ice-shelves a vivid green coloration.

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An iceberg is a section of an ice-shelf that has broken away from the main body of ice. Ice-shelves in both the north and south polar regions are diminishing in size due to global warming, releasing massive volumes of water into the world’s oceans.

ICEBERG FORMATION Ice-shelves and glaciers are grounded on land, while the outer parts float on the sea. The movement of the floating section with the rise and fall of the tides causes great strain, especially where crevices are already present. Huge cracks open up, and chunks of ice break away, which crash into the sea as icebergs – a process known as calving. Some icebergs can be as large as a small country. More than 50,000 large icebergs are calved from Greenland alone each year. Snowfall adds to the thickness of the ice-sheet

Tidal movement causes cracking

Ice-sheet moves towards the sea

Floating section of ice-shelf

Icebergs break away

Sea bear The polar bear lives, hunts, and breeds on sea-ice or in water, coming ashore only when forced by melting ice. The fur loses a large proportion of its insulating properties in water, but the dense underfur still provides some benefit by trapping body heat, ensuring the bear stays warm.

Huge paws act as shovels, snow shoes, and powerful paddles when swimming

Arctic giant An adult male polar bear on two legs stands over 3 m (10 ft) tall and can weigh over half a tonne. Along with the bear’s fur and a layer of blubber, huge size is an adaptation to cope with extreme cold.

Many polar mammals protect themselves from extreme cold by having a coat of fur, but the insulation provided by the fur of effective. It has two layers: a water-repellent outer coat, consisting of long guard hairs, and a dense underfur that keeps the bear warm. The guard hairs are tapered and hollow, making the coat lighter and more buoyant than it would otherwise be. Although polar bears look white, and blend into their Arctic surroundings of snow and ice, their skin is black and their hair is colourless.

COLOUR AND WARMTH The guard hairs of the polar bear’s coat are transparent. Light falling on them is scattered and reflected so that the bear appears white. Like all fur-coated mammals, a polar bear’s metabolism generates heat to keep the body warm and functioning. Most of the insulation is provided by the bear’s underfur, where air trapped between the densely packed hairs helps to stop heat escaping from the body on moving currents of air.

POLAR BEAR FUR AND SKIN

Solar radiation

Heat generated in body by bear’s metabolism

Hollow guard hairs scatter and reflect light

Most heat escaping from body is trapped in underfur

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different animals varies greatly. The fur of the polar bear is highly

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multipurpose fur

spotlight species

narwhal The narwhal (Monodon monoceros) can be easily identified by the impressive tusk that gives rise to its nickname the “unicorn of the sea”. The tusk is in fact a sensitive, elongated tooth that erupts from the side of the animal’s upper jaw.

THE NARWHAL TUSK Nerves deep within the core of the narwhal’s tooth, or tusk, are connected to tiny pores in its outer surface, or cementum, via an estimated 10 million tubules that lie in the dentine layer. When sea water washes through these tubules, specialized cells at their base detect changes in water composition, pressure, and temperature and relay the information to the brain via the tusk’s nerve cells.

Spiral surface on outer layer (cementum)

Layer of dentine around tubules

Hard tissue

Soft tissue

Nerves

Dentine

Veins

Arteries at centre of tusk

NARWHAL TUSK CROSS SECTION

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Coming up for air In winter narwhals congregate, usually in pods of two to 20, in areas of Arctic pack ice. When they surface, like these males at Nunavut, Canada, they are vulnerable to predators such as polar bears.

animal to “read” its environment for the presence of food or mates and measure water salinity. A narwhal does not use its tusk to spear food; instead it uses it to tap and stun its prey, which it swallows whole. Male narwhals become sexually mature around the age of nine years (females mature at six to seven years), when they reach 4–4.5 m (13–15 ft) long and weigh 1,000–1,600 kg (2,200– 3,500 lb). The animals live in the Arctic waters of Russia, Norway, Greenland, and Canada. Around 75 per cent of the world’s population inhabit the biologically rich waters of Baffin Bay and the Davis Strait, between Canada and Greenland. In winter, when the sea turns to pack ice, they can dive up to 1,100 m (3,600 ft) to hunt for deepwater fish such as halibut, before coming to surface at cracks or holes in the ice to breathe.

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Narwhals are classed as toothed whales, but the one or, sometimes, two tusks they grow are their only teeth. The tusks are highly flexible, “inside-out” teeth – soft on the outside, hard and dense towards the core – with millions of nerve endings near the surface. Found mainly in males (only around 3 per cent of females have them), they grow in a counterclockwise spiral throughout an animal’s life. It was once thought a narwhal used its tusk only for defence, but studies show that it is also a sensory organ. Its nerves detect information from the water, helping the

glossary ABDOMEN The hind part of the body of a vertebrate or arthropod.

ANEMONE See Sea Anemone.

BEAK The horny, toothless jaws of a bird, turtle, or cephalopod.

ocean plants such as mangroves, seaweeds, and seagrasses.

BENTHIC Relating to an object or organism living on the seafloor.

BONY FISH The class of vertebrates that includes all living fish except hagfish, lampreys, and sharks and their relatives. These fish have an internal skeleton, which in almost all species is made of bone. See also Cartilaginous fish.

ANTENNA (pl. ANTENNAE) One ABORAL On the opposite side of the

body from the mouth; used especially with reference to animals that have radial symmetry, such as jellyfish and echinoderms. See also Radial symmetry. ABYSSAL A term applied to the depths of the ocean. The abyssal plain is the almost flat plain of the deep ocean floor beyond the continental margin. The abyssal zone is the zone of water between 4,000 and 6,000 m (13,000 and 20,000 ft) deep. See also Hadal zone. ADIPOSE FIN A small, fleshy fin

between the dorsal and tail fins in some bony fish. AERIAL ROOT A root that grows

from, or reaches, a point above ground level, as in many mangrove trees. See also Mangroves. ALGA (pl. ALGAE) Any organism that

photosynthesizes but is not a true plant, including seaweeds and many microscopic forms. Cyanobacteria are usually now excluded from the definition. See also Cyanobacteria. AMPHIPODS An order of mainly small crustaceans that includes sandhoppers and their marine and freshwater relatives. AMPULLAE OF LORENZINI The sensory receptors in the skin of sharks and relatives, located around the head region. They can detect weak electric fields such as those produced by the muscle movements of potential prey. ANADROMOUS Having a life cycle that involves migrating from the sea to fresh water in order to breed, such as in some species of salmon. See also Catadromous. ANAL FIN A single fin on the underside of many fish, near the tail.

of a pair, or in some groups two pairs, of long, thin sensory structures on the heads of arthropods. Antennae are sometimes called “feelers” because of this sensory characteristic. ARTHROPODS The phylum of jointed-legged invertebrates including crustaceans, insects, and spiders. ASEXUAL REPRODUCTION Any form of reproduction that does not involve the fusion of sex cells to create a new individual. An example of this is the budding off of new individuals from a parent, which can occur in marine invertebrates, such as some corals. BACKSHORE The part of the shore lying above the normal high-tide line, reached by the sea only under exceptional conditions. BACKWASH The flow of water back to the sea after a wave has broken. See also Swash. BALEEN A horny material that grows in the mouths of many whales. It takes the form of plates with hairlike fringes that are used in filter-feeding. BANK In oceanography, a submerged

shallow region or plateau of seafloor surrounded by deeper water. BARBEL A fleshy, sensitive feeler, or a longer projection, found near the mouth in some fish, such as catfish and dragonfish. BARNACLES A class of filter-feeding marine crustaceans that live attached to surfaces and have bodies protected by chalky plates. BARRAGE A low dam with sluices

(gates for water) built across a river or estuary. A tidal barrage is designed to trap water at high tide and obtain hydropower when the water is let out.

BILATERAL SYMMETRY Body symmetry in which there is a left and right side, a head, and a tail. See also Radial symmetry. BINOCULAR VISION A type of vision in which objects are viewed from two eyes simultaneously, which allows perception of depth and distance. BIOELECTROGENESIS The creation

of electric fields by living organisms, including some fish. Weak electric fields can be used as a form of echolocation, while strong ones can be used to “shock” other organisms, either in attack or in defence. BIOLUMINESCENCE Production of light by living organisms. Sometimes the light is produced by the organism’s own cells, and in other cases by lightproducing bacteria. BIOME Any group of large-scale ecosystems across the world that display similar features due to shared climatic conditions. The concept is most commonly applied to land ecosystems. BIVALVES A class of molluscs that features a pair of hinged shells. Bivalves include clams, mussels, scallops, oysters, and relatives. BLACK SMOKER A type of hydrothermal vent in which the hot water is coloured dark by sulphide minerals. See also Hydrothermal vent. BLOWHOLE The nostrils of a whale

or dolphin, found on the top of the head. The blowhole may be single or double depending on the species. BLUE CARBON Carbon that is removed from the atmosphere by

BREAKWATER A long, solid structure built into the sea to protect a harbour from rough ocean conditions. CALCAREOUS Containing or made of calcium carbonate. CALYX In zoology, the cuplike structure of a sea lily or feather star. CAMOUFLAGE Features of an organism that make it difficult to detect visually against its natural background, including colour patterns and aspects of body shape. CARAPACE The protective shield covering the upper surface of a turtle, crustacean, or horseshoe crab. CARRION Animal matter that is dead or decaying. CARTILAGINOUS FISH A class of fish whose skeleton is made of cartilage, not bone. It includes sharks, rays, and chimaeras. CATADROMOUS Having a life cycle that involves migrating from fresh water to the sea in order to breed. See also Anadromous. CAUDAL FIN The tail fin of a fish. CELLULOSE A fibrous carbohydrate that is the main structural substance of plants, many algae, and also tunicates. Animals that consume cellulose through eating plant matter can normally only digest it with the aid of symbiotic bacteria in their gut. See also Symbiosis, Tunicates.

CEPHALOPODS A class of tentacled molluscs that includes squid, cuttlefish, octopuses, and nautiluses.

CIGUATERA Poisoning from eating toxic sea food, often caused by consuming fish that have eaten toxic dinoflagellates. See also Dinoflagellates.

CONTINENTAL RISE The region where the deep ocean seabed begins to get shallower at the edge of a continental margin.

CILIA (sing. CILIUM) Microscopic

CONTINENTAL SHELF The relatively flat and shallow seafloor surrounding a continent, which is geologically part of that continent.

CEPHALOTHORAX The fused head

and thorax of a crustacean or a spider. CHELA A pincer, especially one belonging to an arthropod such as a crab. A chelate leg is a leg with a pincer at the end of it.

beating hairs on the surface of some cells, found on animals such as fan worms. These hairs are used for locomotion or to generate currents. CIRRI (sing. CIRRUS) Small, stiff,

carbohydrate material that forms the skeletal parts of some animals, including the exoskeletons of arthropods. It usually mixes other materials to increase its hardness and strength. See also Exoskeleton.

CLASPERS In sharks and their relatives, the modified pelvic fins of the male that transfer sperm to the female’s body during copulation. See also Pelvic fins.

CONVECTION Circulating movements in a fluid caused by heat being applied to parts of it. This results in warmer and therefore less dense fluid rising upwards, which drives the circulation. COPEPODS A class of small

CLASS A category in biological classification. It is above an order and below a phylum. See also Order, Phylum. CLOACA A combined body outlet

for urinary products, faeces, and reproductive cells, found in most fish and birds.

swimming crustaceans that form an important part of the plankton. CORALLITE The cup-shaped skeleton of aragonite below the body of an individual coral polyp. COUNTERSHADING Coloration of an animal’s body that helps to disguise it by counteracting the effect of shadows, usually by being lighter on the underside of the body.

CHLOROPHYLL The green pigment

CNIDARIANS A phylum of

that plants, algae, and some other organisms, including cyanobacteria, use to trap the Sun’s energy for use in photosynthesis. There are several different types of chlorophyll. See also Cyanobacteria, Photosynthesis.

invertebrate animals with stinging tentacles that includes sea anemones, corals, jellyfish, and relatives.

coast, Submergent coast.

CRUSTACEANS A subphylum of arthropods including crabs, lobsters, shrimps, barnacles, and copepods.

CHORDATES A phylum of animals that includes all the vertebrates as well as some invertebrate relatives, including tunicates. See also Tunicates.

COMPOUND EYE An eye consisting of many small individual facets packed together. Compound eyes are a common type of eye in arthropods.

CRYPSIS Features or behaviours that allow an animal to avoid detection. Crypsis includes concealed habitats, camouflage, or nocturnal behaviour.

CHROMATOPHORE A pigment-

CONTINENTAL CRUST The part of

containing cell or group of cells in the skin of many animals. Different types of chromatophores display different colours. Animals with chromatophores can adjust the distribution of pigments within individual cells, altering their overall appearance. See also Cyanophore, Iridophore.

Earth’s crust that forms the continents. It is less dense and thicker than oceanic crust. See also Oceanic crust.

COAST See Emergent coast, Erosional

CONTINENTAL MARGIN The region of seafloor surrounding a continent, including the continental shelf, continental slope, and continental rise.

CYANOPHORE A blue chromatophore. See also Chromatophore. DEPOSIT FEEDER An animal that feeds by extracting food particles from mud or sand. DETRITIVORE An animal whose food consists of small fragments of dead material (detritus). DIATOMS A group of microscopic single-celled organisms featuring an ornamented, boxlike protective covering. Most are photosynthesizers and live near the water surface as plankton, where they form an important part of many marine food chains. See also Photosynthesis, Phytoplankton, Plankton. DINOFLAGELLATES A group of microscopic single-celled organisms with two flagella that help them move, many of which are photosynthetic and live near the surface as plankton. See also Flagellum, Photosynthesis, Plankton. DORSAL Relating to the upper side or back of an animal. See also Ventral. DORSAL FIN A fin situated on the back of a fish or whale.

DOWNWELLING The sinking down of water from the surface of the ocean. Large-scale downwelling in certain Camouflage, Crypsis. regions gives rise to a process known CTENOPHORES A jellyfishlike phylum as thermohaline circulation. See also Thermohaline circulation, Upwelling. of floating carnivorous animals, also called comb jellies. DRIFT A large-scale flow of surface water that is broader and slowerCURRENT A regular large-scale moving than a current. horizontal or vertical flow of ocean CRYPTIC COLORATION See

glossary

CHITIN A nitrogen-containing

hairlike projections in some animals, often used for grasping or movement. They are found, for example, in sea lilies and feather stars.

CYANOBACTERIA An abundant group of microscopic photosynthesizing bacteria, formerly called blue-green algae. Their tiny cells lack nuclei, as do those of other bacteria. See also Alga, Protists.

320 • 321

CHEMOSYNTHESIS The process by which an organism can grow and multiply using the energy stored in simple chemicals such as hydrogen sulphide or methane. Chemosynthesis functions in contrast to photosynthesis, which depends on energy coming from the Sun. Many bacteria can carry out chemosynthesis, notably those living around hydrothermal vents. See also Hydrothermal vent, Photosynthesis.

CONTINENTAL SLOPE The sloping seabed that leads from the edge of a continental shelf down to the continental rise.

water in one direction; also a smaller flow of water near the shoreline.

DUNE A mound of sand formed by the action of winds blowing towards coastal land.

FAST ICE Sea-ice that is frozen on to the coast or land-formed ice at its landward edge. See also Sea-ice.

ECHINODERMS A marine

FILTER-FEEDER An animal that feeds

invertebrate phylum that includes starfish, sea urchins, sea cucumbers, and relatives. These animals feature tube feet that enable some of them to walk. See also Tube feet.

by filtering small food particles from its environment, through the baleen in the case of some whales. Filterfeeders are a type of suspension-feeder. See also Baleen, Suspension-feeder.

ECHOLOCATION A method of detecting and locating objects, which is used by dolphins and some other animals. Sound waves are emitted and their echoes are then gathered and interpreted. See also Melon.

FJORD An inlet of the sea once occupied by a glacier. Fjords are often deep and steep-sided, with a shallower sill at their mouth. See also Glacier. FLAGELLUM (pl. FLAGELLA) A long,

land has risen relative to the current sea level. See also Submergent coast.

microscopic whiplike structure used by some single-celled organisms, such as dinoflagellates, for locomotion. See also Dinoflagellates.

ENDOPARASITE A parasite that lives

FLIPPER A limb used for swimming,

inside the body of another organism. See also Parasite.

for example in whales, seals, penguins, and turtles.

ENDOSKELETON A skeleton that is

FLUKE Either of the two flattened sides

inside the body rather than on the surface, such as the skeletons of vertebrates and echinoderms.

of a whale’s tail.

EMERGENT COAST A coast where the

EPITHELIUM A layer of living cells

on the surface of an animal’s body or of an internal organ. EROSIONAL COAST A coastline that is

gradually being eroded by the sea. EURYHALINE Able to survive in water

of a wide range of salinities. See also Salinity, Stenohaline. EXOSKELETON A skeleton on

the outside of the body, such as the skeletons of arthropods. EXTERNAL FERTILIZATION

Fertilization in which egg and sperm combine outside the body, usually in sea water. See also Internal fertilization. FAMILY A category in biological classification. It is above a genus and below an order. See also Genus, Order.

FORAMINIFERANS Single-celled organisms that mainly live on the seafloor, protected by chalky shells, and feed on other small organisms. FRAZIL ICE Ice that forms in cold water and consists of thousands of tiny crystals. It is an early stage in the development of sea-ice and in turbulent waters it can form pancake ice. See also Pancake ice, Sea-ice. FROND A flattened, leaflike structure found in many seaweeds. Unlike the leaves of land plants, seaweed fronds do not contain specialized transport vessels to interchange materials with the rest of the organism. GASTROPODS The largest class of molluscs, which includes all snails and slugs. GENUS (pl. GENERA) A category

in biological classification. It is above

a species and below a family. The scientific name of a species consists of two words: a genus name and a species epithet. For example, Ursus maritimus, the polar bear, is a species in the genus Ursus, which also includes other bears. See also Family, Species. GILL A structure for absorbing oxygen from water, often found in fish, molluscs, and crustaceans. Gills can also have other functions such as sieving small food particles.

chemicals issues from the rock at high temperatures. HYDROZOANS A class of mainly colonial cnidarians that includes hydroids, siphonophores, and some small jellyfish. See also Cnidarians, Hydroids, Jellyfish, Siphonophores. ICE-SHEET A very large area of ice that permanently covers a land area, as in Antarctica or Greenland.

GLACIER A “river” of ice that flows

ICE-SHELF A floating extension of an ice-sheet or glacier over the ocean.

slowly downhill from an ice cap or mountainous region.

INTERNAL FERTILIZATION

GUYOT A sea mount with a flat top.

See also Sea mount.

Fertilization where the eggs and the sperm meet and fuse inside the body of an animal. See also External fertilization.

GYRE A large system of ocean currents circulating round a centre point. There are five major ocean gyres.

INTERTIDAL Between the high and low water marks of a shoreline.

HADAL ZONE The deepest zone of ocean water, below 6,000 m (20,000 ft), which occurs only in ocean trenches. See also Abyssal.

INVERTEBRATE Any animal other than a vertebrate without a backbone, such as tunicates and arthropods. See also Vertebrates.

HERMAPHRODITE An animal that is both male and female. A simultaneous hermaphrodite is male and female at the same time, while a sequential hermaphrodite changes from one sex to the other, either once or repeatedly.

IRIDOPHORE A reflective or iridescent kind of chromatophore. See also Chromatophore.

HOLDFAST The structure that holds a seaweed to the seafloor. It is not a true root because it does not absorb substances for use in the rest of the body. HOST Any organism on which a given parasite regularly feeds. HYDROIDS A subgroup of hydrozoans that usually grow as small, plantlike colonies of connected individuals. See also Hydrozoans. HYDROTHERMAL VENT A fissure in a volcanically active area of the ocean floor, where water rich in

ISOPODS An order of mainly small crustaceans that includes woodlice, sea slaters, and many marine species. JELLYFISH Members of the cnidarian class Scyphozoa, whose adults drift or swim slowly in the ocean and use stinging cells to subdue prey. The deadly “box jellyfish” are a separate but related class, and the word can also be used for the small medusas of hydrozoans. Despite their name jellyfish are not, in fact, fish. See also Cnidarians, Hydrozoans, Medusa. KERATIN A tough protein that forms the substance of claws, nails, and hair. KINGDOM The highest category in traditional biological classification.

KRILL An order of shrimplike planktonic crustaceans that form a major part of ocean food chains, especially in the Southern Ocean. See also Plankton.

MANTLE The fleshy covering on the outside of the body of molluscs and brachiopods that secretes the shell. Mantle can also refer to the rocky layer of Earth between the crust and the core.

LAGOON An enclosed area of coastal

water almost cut off from the sea by a barrier, or the sea area within the ring of an atoll. LARVA The young stage of an animal

when it is very different in structure from an adult. LATERAL LINE SYSTEM A sensory

LICHEN A “double organism” in

LONGSHORE DRIFT Process by which sediments such as sand and mud are transported along the coastline as a result of sea waves breaking at an oblique angle to the shore. MAMMALS A class of warm-blooded vertebrates that almost all give birth to live young and nourish them using milk produced by the female. Marine mammals include seals, whales, manatees, and sea otters. MANDIBLE The lower jaw of vertebrates, or the biting or crushing mouthparts of many arthropods. See also Arthropods. MANGROVES Salt-tolerant trees that grow in sheltered intertidal zones in warmer regions and whose roots are regularly covered by sea water. The term “mangroves” can also refer to the ecosystems and forests that feature such trees.

MELON A structure containing fatty tissue, found in the head of dolphins and other toothed whales, that plays a role in emitting sound for communication and echolocation. See also Echolocation. METAMORPHOSIS A major rearrangement of body structures that occurs during the development of some animals.

NOTOCHORD A stiffening rod that runs the length of the body in chordate animals. In most vertebrates it is replaced by the backbone early in embryonic development. See also Chordates. NUTRIENTS Chemicals, especially salts of elements such as nitrogen, phosphorus, and iron, that are essential for living organisms to grow.

MID-OCEAN RIDGE An undersea mountain range running along the deep ocean floor where new oceanic crust is created.

OCEAN One of the huge bodies of salt water that between them cover almost 70 per cent of Earth’s surface. They are normally listed as the Atlantic, Pacific, Indian, Arctic, and Southern (or Antarctic) oceans, but as they are all connected they are also sometimes referred to as the World Ocean.

MIMICRY A detailed resemblance between an animal and something else, especially another animal, for the purposes of disguise or deception. See also Camouflage.

OCEAN ACIDIFICATION An increase in the acidity of ocean waters, especially as a result of dissolved carbon dioxide as a consequence of human activities.

MOLLUSCS A major phylum of softbodied but usually hard-shelled invertebrate animals that includes gastropods, bivalves, and cephalopods.

OCEAN BASIN A region occupied by a deep ocean or part of one, consisting of low-lying oceanic crust surrounded by shallower water or land.

MUTUALISM An association between members of two different animal species in which both benefit. The association between cleaner shrimps and moray eels is an example of this. See also Symbiosis.

OCEANIC CRUST Earth’s crust under the deep oceans, which is thinner and denser than the crust of the continents. See also Continental crust.

NEKTON Organisms that live in

OMMATIDIA (sing. OMMATIDIUM) The individual eye-facets in a compound eye. See also Compound eye.

open water and swim strongly enough to move directionally, rather than being at the mercy of currents. See also Plankton.

OPERCULUM The external covering of a gill of a bony fish. It can also refer to a hard disc that seals the opening

OPISTHOSOMA The hind-part of the body of a horseshoe crab or spider. ORDER A category in biological classification. It is above a family and below a class. See also Class, Family. OSSICLES The tiny calcareous units that connect together to form the skeleton of an echinoderm. PACK ICE Floating sea-ice that is not attached to land. It may be fused together in a single mass or consist of separate ice floes. PALPS In arthropods and some other invertebrates, palps are paired, jointed structures near the mouth, typically with a sensory function. In bivalves, they are a pair of fleshy structures close to the mouth. PANCAKE ICE A stage in the formation of sea-ice in turbulent waters consisting of separate floating plates. Pancake ice plates have raised, rounded edges as a result of colliding with other plates. See also Sea-ice. PARASITE An organism that lives on, or in, another larger organism and feeds from it for an extended period of time. PECTORAL FINS A pair of fins attached to the chest, towards the front of a fish, behind the gills, one on each side. PELVIC FINS A pair of fins in fish, attached to the abdomen, further back and lower down than the pectoral fins. PHOTOPHORE A light-producing organ found in some fish, cephalopods, and other animals. Complex photophores may feature lenses and colour filters. See also Bioluminescence.

glossary

which a fungus’s body is combined with algal cells. Although essentially land organisms, some lichens are tolerant of sea spray and thrive on higher levels of rocky shores.

of cnidarian animals. A medusa is a floating, usually saucer-shaped body form with a central mouth on the underside and tentacles. Jellyfish are medusas. See also Cnidarians, Polyp.

NEUROMAST One of the small sensory structures that form part of the lateral line system in aquatic vertebrates. See also Lateral line system.

of a snail’s shell when the animal withdraws its body inside.

322 • 323

system that runs along the sides of the body in fish and some other aquatic vertebrates. It is used to detect movement and pressure changes in the surrounding water.

MEDUSA One of the main body forms

NEMATOCYST The stinging cell of a cnidarian that acts like a tiny harpoon. It is usually charged with venom. See also Cnidarians.

PHOTOSYNTHESIS The process by which plants, algae, and cyanobacteria use the Sun’s energy to convert water and carbon dioxide into carbohydrates, as a first step to building up their body structure and trapping energy for cell processes. See also Chemosynthesis. PHYLUM (pl. PHYLA) A category in

biological classification, above a class and below a kingdom. Examples of phyla include cnidarians, molluscs, arthropods, and chordates. See also Class, Kingdom. PHYTOPLANKTON Planktonic

man o’ war have a gas-filled float that is also known as the pneumatophore. See also Siphonophore. PODIA (sing. PODIUM) Small

hydraulically operated structures on the surface of echinoderms, used for respiration or movement. Podia for walking and grasping usually have suckered ends and are called tube feet. See also Tube feet, Water-vascular system.

RADIOLARIANS A group of singlecelled organisms that float in the plankton and act like tiny animals, feeding on other small life-forms. They have elaborate skeletons of silica, often spherical in shape. RADULA A belt-shaped rasping organ found in the mouths of many molluscs and equipped with horny teeth. REFRACTION The change of direction

POLYP One of the main body forms of cnidarians, consisting of an attached cup-shaped body with a mouth on the top surface surrounded by tentacles. A sea anemone is a polyp. See also Cnidarians, Medusa.

of waves, including light waves, when they pass from one medium to another, and water waves when they reach shallow water.

organisms that photosynthesize, mainly microscopic algae and cyanobacteria. See also Alga, Cyanobacteria, Plankton.

PREDATOR An animal that catches and eats other animals.

RHIZOSPHERE The region of soil or

PINCER A claw or similar structure

PREY Animals that are food for a

mud around a root that is influenced by the root’s activities and metabolism.

for grasping objects and for attack and defence.

given predator within a food chain. PROSOMA A word for cephalothorax,

PLANKTON All the life-forms that drift in the open ocean and are carried along by ocean currents. See also Nekton. PLATE BOUNDARY A boundary

between two of Earth’s tectonic plates. A constructive (or divergent) boundary is where two plates are being pushed apart by new molten rock rising between them, as at midocean ridges. At a destructive (convergent) boundary, two plates are pushed together, often with one being subducted beneath the other. See also Subduction. PLATE TECTONICS All the processes relating to the movement and collision of the enormous tectonic plates into which Earth’s crust and upper mantle are divided. See also Mid-ocean ridge, Subduction. PNEUMATOPHORE Part of a

mangrove plant root that is exposed above the ground and can absorb air. Siphonophores, such as the Portuguese

especially in horseshoe crabs and spiders. See also Cephalothorax. PROTANDRY A form of

hermaphroditism where an organism is first male, then female. See also Hermaphrodite, Protogyny.

RHIZOME A horizontal underground stem of a plant.

ROOKERY A breeding colony of penguins, and sometimes of other seabirds or seals. SALINITY The degree of saltiness of sea water. SALPS Free-floating colonial tunicates that consume phytoplankton. See also Phytoplankton, Tunicates.

PROTISTS A broad category covering

organisms that are not classified as animals, plants, or fungi. Most are microscopic, although traditionally seaweeds are also included. Protists all have cells with nuclei and so do not include cyanobacteria. See also Cyanobacteria. PROTOGYNY A form of hermaphroditism where an organism is first female, then male. See also Hermaphrodite, Protandry. RADIAL SYMMETRY The form of symmetry exhibited by a star-shape, as opposed to one with left and right sides. Sea anemones, starfish, and sea urchins have radial symmetry. See also Bilateral symmetry.

SALT MARSH An ecosystem that may develop on the upper intertidal zone of sheltered, muddy coastlines, mainly in cooler parts of the world, and consists of a community of small, salt-tolerant land plants. In the tropics, mangrove forests generally grow in similar situations. See also Intertidal, Mangroves SCALES Small, often overlapping

protective structures on the skin of fish, reptiles, and some invertebrates. SEA Sometimes used as another word for ocean, but can also refer to a relatively small, often shallower region of an ocean partly marked off by land, such as the North Sea.

SEA ANEMONES An order of solitary soft-bodied cnidarians that have only a polyp stage, also referred to simply as “anemones”. See also Polyp. SEA-ICE Ice formed directly on the sea, as distinct from icebergs and iceshelves, which originally formed on land before entering the sea. SEAGRASS One of many flowering grasslike plants in the order Alismatales that have become adapted to live under saline water. SEA MOUNT An undersea mountain, usually formed by volcanic activity. See also Guyot. SEAWEEDS Any of several groups of relatively large marine, plantlike organisms traditionally classified as multicellular algae. One group, the green seaweeds, is closely related to land plants. SEDIMENT Particles carried in water that are capable of settling out under the force of gravity, or deposits formed by such particles, including sand, silt, or mud. SEXUAL REPRODUCTION

Reproduction involving the fusion of two sex cells (typically an egg and sperm) followed by development of a new individual from the fertilized egg. See also Asexual reproduction. SHELL The hard protective covering of animals such as molluscs, brachiopods, and turtles. Also, the outer covering of an egg. SIPHON A tubelike structure that draws in or expels water. Bivalve molluscs and tunicates have a pair of siphons, which are used for filterfeeding as well as obtaining oxygen from the water. SIPHONOPHORES An order of floating colonial hydrozoans resembling jellyfish, that includes the

Portuguese man o’ war. See also Hydrozoans, Jellyfish.

SUBTIDAL Below the lowest level of the tides on a shoreline.

SPAWN Masses of small eggs released by many marine animals. “To spawn” is to release these eggs.

SUCKER A structure used by an animal to attach to a surface.

SPECIES A particular kind of

organism, such as a polar bear or an emperor penguin. If a species reproduces sexually it can be defined as comprising individuals that are able to breed with each other to produce fertile offspring that resemble their parents. See also Genus.

SURFACE CURRENT A current at the ocean surface, usually driven by wind. SUSPENSION-FEEDER An animal that feeds by extracting small food particles suspended in the water. Filter feeding is a form of suspension feeding. See also Filter-feeder. SWASH Moving of turbulent water

SPONGES A phylum of simple-bodied

TAGMA (pl. TAGMATA) One of the

main sections into which the bodies of arthropods and some segmented worms are divided. TELSON The hindmost segment of an arthropod. In crustaceans such as lobsters and some crabs, it forms the central part of the tail fan.

slow-moving animals that live by straining food particles from the water. TENTACLE A long, fleshy structure used for capturing food or other purposes. Many marine invertebrates STENOHALINE Able to tolerate only have multiple tentacles. a narrow range of salinities. See also Euryhaline, Salinity. THERMOCLINE Any layer at a particular depth in an ocean where the SUBDUCTION The process in which average temperature changes rapidly the oceanic crust of one tectonic plate with depth. Thermoclines can also is slowly forced under the edge of occur in the atmosphere. another plate. See also Oceanic crust, Plate tectonics, Trench. THERMOHALINE CIRCULATION SUBMERGENT COAST A coast where

the land surface has become lower relative to the current sea level. See also Emergent coast.

A worldwide circulation of deepwater currents driven by differences in temperature and salinity between different water masses.

TISSUE An assemblage of cells of a particular type in the body, such as nervous tissue or muscle tissue. Organs are formed of different types of tissue combined together. TRENCH A large-scale, naturally forming chasm on the ocean floor where the ocean is deepest and one tectonic plate is forced under another. The deepest is the Mariana Trench in the Pacific Ocean. See also Subduction. TROPICAL CYCLONE A large-scale circulating weather system in tropical and subtropical regions, powered by warm ocean water and producing violent winds and heavy rain. Also known as hurricanes, typhoons, or simply as cyclones depending on which part of the world they occur in. TSUNAMI A large, fast-moving ocean wave generated by an undersea earthquake or a large coastal landslip. TUBE FEET Another name for the podia of echinoderms, especially when they have suckered ends and are used for walking or clinging. See also Podia, Water-vascular system. TUNICATES A subphylum of invertebrate animals that are related to vertebrates and include the sea squirts and salps. See also Chordates. TUSK An enlarged tooth of a mammal such as a walrus or narwhal. UPWELLING The rising of deep ocean water to the surface. It can be caused

VALVE Either of the two hinged shells of a bivalve mollusc. VENTRAL Relating to the front or underside of an animal. See also Dorsal, Invertebrate. VERTEBRATE A backboned animal. Forming a subphylum of the phylum Chordata, vertebrates include fish, amphibians, reptiles, birds, and mammals. See also Chordates. WARNING COLORATION The coloration of an animal signalling to predators that the animal is poisonous or venomous. WATER-VASCULAR SYSTEM The hydraulic system of echinoderms, which operates their tube feet (podia). See also Podia, Tube feet. WHISKER A stiff, modified hair on the face of a mammal. The “whiskers” of catfish are actually long, thin barbels. See also Barbel. ZOOID An individual unit of a colonial invertebrate animal that is physically connected by strands of tissue to other individuals. The term is used in connection with moss animals and tunicates but not cnidarians. ZOOPLANKTON Animals and animallike organisms living in the plankton. See also Plankton, Protists. ZOOXANTHELLAE Symbiotic dinoflagellates that live in the bodies of many corals and some other animals and create food for them by photosynthesis. See also Dinoflagellates.

glossary

SPIRALIANS A large group of invertebrate phyla all thought to be related, named after the spiral pattern of early cell divisions in their fertilized eggs. Spiralians include molluscs, lamp shells, segmented worms, ribbon worms, and others.

TIDE The regular variation in the height of the ocean surface at a given point, caused by the gravitational attraction of the Moon and Sun combined with Earth’s rotation. In coastal regions, it results in horizontal movements of water.

by wind blowing parallel to a coastline or by an underwater obstruction such as a sea mount interrupting a deepsea current. Upwelled water often enriches the surface of the ocean with nutrients. See also Downwelling.

324 • 325

up a shoreline after a wave breaks. units embedded in the bodies of many sponges and some cnidarians. Spicules SWIM BLADDER A gas-filled structure come in many shapes and sizes and are in most bony fish that regulates the important in sponge classification. buoyancy of the fish and stabilizes it in the water. SPIRACLE One of the openings behind the eyes of a ray through which water SYMBIOSIS The close association for the gills enters. The term is also between two kinds of animal. When applied to other structures such as the this is mutually beneficial, it is called breathing holes of insects. mutualism. See also Mutualism. SPICULE One of the small skeletal

THORAX The chest region of a vertebrate, or the central region of the body of an arthropod.

index Page numbers in bold refer to main entries

A

Aboriginal art 164–65 abyssal plain 265 abyssal zone 19 Acanthaster planci (crown-of-thorns star) 223 Acanthocardia echinata (prickly cockle) 80 Acanthurus mata (elongate surgeonfish) 175 acidity levels effect on coral 140 effect on shells 297 kelp forests and 189 Acropora cervicornis (staghorn coral) 134 Acropora cytherea (table coral) 135 Acropora palmata (elkhorn coral) 134 Acropora sp. (stony coral) 126–27 Actinia equina (beadlet anemone) 30–31 adhesive chemicals 25, 221 adipose cells 308 adventitious roots 28 Aegean Sea 181 Aeginopsis laurentii (golf tee jelly) 270 aeolid nudibranchs 210–11 aeolid sea slugs 148 Aequorea victoria (crystal jelly) 192–93 Age of Exploration 281 Aivazovsky, Ivan 71 Alatina alata (winged box jelly) 270 albatross, wandering 286–87 Alca torda (razorbill) 55 algae on anemones 138, 167 benthic 175 on coral 126, 130, 132, 183 on giant clams 147 giant kelp 188–89 ice-shelves 314 lichens 22 mangrove roots 105 phytoplankton 258 polar regions 301 on rocks 34, 35 symbiotic 106, 126, 136 on zoanthids 142 see also seaweeds alkaloids 142, 143 Allostichaster palmula (paddle-spined sea star) 222 Amblyrhynchus cristatus (marine iguana) 50–51 ambush tactics 233, 276 American crocodile 72–73 ammonites 14–15 Ammophila arenaria (common marram grass) 62–63 Amphioctopus marginatus (coconut octopus) 40 amphipod, giant 19 ampullae 221 ampullae of Lorenzini 89, 226 anadromous fish 90 anchovies 239

anemones anatomy 199 beadlet 30–31 dahlia 138 daisy 30 firework tube 198–99 Haddon’s carpet 138–39 jewel 30 life cycle 129 mutualistic relationships 166 nutrition 136 plumose 30 Triactis 157 tube 199 angelfish, emperor 46 anglerfish 19 Anglo-Dutch War 94 Anguilla anguilla (European eel) 46 anguilliform fish 46 annelid worms 145, 200–01 antennae American lobster 213 crabs 41, 115 golden fireworm 200 isopods 266 krill 301 scarlet skunk shrimp 154 Antennarius maculatus (warty frogfish) 46 anthius, flame 184 Anthomastus (mushroom coral) 135 antifreeze proteins 303 Aporia crataegi (black-veined white butterfly) 28 Aptenodytes forsteri (emperor penguin) 307 Aptenodytes patagonicus (king penguin) 306–07, 311 aragonite 297 archerfish, banded 116–17 arches 27 Architeuthis (giant squid) 267 Arctic Ocean 12 Arctic tundra 92 Arenaria interpres (ruddy turnstone) 92 argonite 134 Argopectan irradians (bay scallop) 202–03 Arg yropelecus olfersii (deepsea hatchetfish) 305 ark shell 80 Armeria maritima (sea thrift) 28–29 armour lobster 212 sea butterfly 297 western Atlantic giant isopod 266 arms brittle stars 218 common sun star 220–21 cuttlefish 205 European squid 208, 209 feather stars 214, 215 gorgon stars 268 octopus 150, 151 starfish 222–23, 268–69 Arnhem Land 165 art 19th-century US 32–33 Aboriginal 164–65 ancient 180–81 Asian sea deities 196–67

art continued Dutch Golden Age 94–95 Fauvism 52–53 Impressionism 118–19 Japanese woodcuts 216–17 maps 280–81 natural history illustration 152–53 Photorealism 64–65 Romantic movement 70–71 arthropods 212 asexual reproduction coral 129 turtle seagrass 190 astaxanthin 154 Astrocaneum spinosum (spiny gorgon star) 268 Atlantic Ocean 12, 15 atolls, coral 141 Aurelia limbata (brownbanded moon jelly) 271 avalanches 76 Avicennia mangroves 107

B

Backhuysen, Ludolf 94 bacteria and detritus 159 hydrothermal vents 262, 263 Balaenoptera musulus (blue whale) 288–89 baleen plates 288 Balistapus undulatus (orange-lined triggerfish) 184 Balistoides conspicillum (clown triggerfish) 178–79 balloonfish 162 bannerfish 170 barbels 44, 236–37, 283 barbs, stingrays 84 bark paintings 165 barnacles 36–37 acorn 38–39 Montagu’s stellate 39 barracudas, chevron 230–31 barramundi 165 barrier islands 68 barrier reefs 141 basal lamina 167 basalt 265 Bathynomus giganteus (western Atlantic giant isopod) 266–67 Baudelaire, Charles 71 beaches 68–69 life on 74–75 sandy 60 beak diamondback terrapin 121 excavating parrotfish 182, 183 pale snipe eel 47 bear, polar 316–17 bells cubozoa 270 jellyfish 109, 193 benthic fish 184–85 Berghia norvegica (nudibranch) 210 Bering Sea 12

Berry Islands 18–19 betacyanin 102 Bierstadt, Albert 33 billfish 285 bills adaptations 92 brown pelican 242, 243 horned puffin 54 osprey 99 razorbill 55 rockhopper penguin 57 sailfish 284, 285 short-billed dowitcher 92 spoonsbill 97 wandering albatross 286 bioelectrogenesis 233 bioluminescence 19, 192–93, 267, 271, 282–83 phytoplankton 258 red 283 biomass, marine 301 Birgus latro (coconut crab) 212 bivalves 80–1, 147, 202 blacksmith damselfish 189 bladed fish 172–73 Blaeu, Joan 281 blennies hair-tail 46 striped 175 blood, antifreeze proteins 303 blood stars, Pacific 222 blubber cetaceans 308 polar bear 317 seals 310, 313 walrus 308 blue, in nature 160–61 bony fish fins 49, 178–79 swim bladders 230–31 boobies 240 Bothus leopardinus (Pacific leopard flounder) 46 Boudin, Eugène 118 Étretat. The Cliff of Aval 118 Braque, Georges 52 Port-Miou 52–53 breaking, waves 43 breathing American crocodile 72 mangrove roots 107 southern elephant seal 310 stingrays 85 breeding sites gannets 56 humpback whales 248 salmon 90–91 bristlemouth 279 bristles, annelids 201 bristleworm 304 brittle stars 25, 268 European common 218–19 Brotulotaenia nielseni (cusk-eel) 304–05 brown seaweeds 186 Bruguiera mangroves 107 bubble-net feeding 248 bubble-rafts 260–61

buoyancy and body size 267 bony fish 230–31 cuttlefish 204–05 eggs 279 lobsters 212 osprey 99 violet snails 261 butterfly, black-veined white 28 butterflyfish bannerfish 170 copperband 171, 184 lined 170 yellow longnose 170 by-the-wind sailor 261

C

coral atolls 141 coral reefs 140–41 feeding on 170–71 reef fish 174–75 sponges 124 symbiotic relationships 154–55 coralivores 170–71 Corallina 187 corallite 127 Coriolis, Gaspard-Gustave de 275 Coriolis effect 206, 274, 275 Corphella verrucosa (nudibranch) 210–11 Corynactis viridis ( jewel anemone) 30 Coryphopterus hyalinus (glass gobi) 184 Coscinodiscus counter-illumination 282 crabs anatomy 41 box 304 coconut 212 hermit 40–41 mangrove horseshoe 110–11 pom-pom 157 red-jointed fiddler 114–15 spider decorator 156–57 velcro 157 Cranchia scabra (glass squid) 305 Cretaceous period 14, 15 crocodile, American 72–73 Crocodylus acutus (American crocodile) 72–73 cross-fertilization 191 cross-flow filtration 273 Crossaster papposus (common sun star) 220–21, 222 crustaceans 212 appendages 115 krill 300–01 crypsis 176, 233 cryptobenthic fish 184 ctenidia 147 Cubism 52 cubozoa 270 curlew, far eastern 92 currents 274–75 and climate 16 and coastal erosion 27 upwelling and downwelling 250 cushion stars 222 honeycomb 223 Panamic 222 cusk-eels 304–05 cuttlebone 205 cuttlefish buoyancy 204, 205 colour change 151, 204 elegant 205 flamboyant 204–05 Cyanea capillata (lion’s mane jellyfish) 271 cyanobacteria 258 cyanophores 160 cysts 136

D

day octopus 150–51 dead material, recycling 158–59 Dead Sea 112–13 decapod crustaceans 115 deepsea currents 274 Dendrog yra cylindrus (pillar coral) 135

index

clownfish 167 common 168 maroon 166–67 cnidarians 138, 270–01 coastal erosion 26–27 coastal seas 184–253 cockles, prickly 80 cod, Atlantic 46 coenenchyme 132 Cole, Thomas 33 collagen 125, 308 collar-flagellate cells 125 Colochirus quadrangularis (thorny sea cucumber) 158–59 colonialism 71 colonies cliff-nesting birds 54–55 coral 127, 129, 130, 132–35, 136 gannetries 56 ground-nesting birds 85 horned puffin 55 hydrozoans 261 king penguins 307 phytoplankton 258–59 siphonophores 256 southern elephant seals 310–11 tunicates 105 zoanthids 142 colour cryptic 233 nudibranchs 210 reef fish 175 seaweeds 186–87 as warning signal 142, 149, 204, 282 colour change cephalopods 151 day octopus 150–51 harlequin ghost pipefish 176–77 ribbon moray 168–69 Colpophyllia natans (boulder brain coral) 135 comb jellies 192 common box jelly 270 compressiform fish 46 cone snails 201 continental plates 290 continental shelf 76 Copernicus, Nicolaus 281 coral 126–27 bleaching 136 boulder brain 135 carnation 134 cold-water 19 colonies 132–33 colourful sea rod 130–31 elkhorn 134 fire hyrdocorals 136–37 fossil 15 gorgonians 131, 135, 162–63, 176 Kenyan tree 134 leather 132–33 mushroom 135 organ-pipe 131 pillar 135 sea pen 135 sexual reproduction 128–29 soft 131, 134–35 spaghetti finger leather 135 staghorn 134 stony 126–27, 134–35 table 135 tube 135 types of 134–35

326 • 327

Calappidae 304 calcium carbonate 127, 134, 145, 212 Calidris pygmaea (spoon-billed sandpiper) 92 Calliostoma zizyphinum (painted topshell) 34–35 calyx 215 Cambrian period 111 camouflage antlered sculpin 302 flamboyant cuttlefish 204 harlequin ghost pipefish 176–77 hooded plover eggs 75 light as 282 nudibranchs 210 short-billed dowitcher 93 southern stingray 84 spider decorator crab 156–57 stargazers 233 stonefish and scorpionfish 86 Camposcia retusa (spider decorator crab) 156–57 Capnella imbricata (Kenyan tree coral) 134 Caranx melampygus (bluefin trevally) 175 carapace American lobster 213 crabs 41 hermit crab 40 horseshoe crab 110 shrimps 262 carbon dioxide carbon sinks 189, 190, 258, 288, 297 hydrothermal vents 262 increased atmospheric 16 Carcharodon carcharias (white shark) 276–77 Carcinoscorpius rotundicauda (mangrove horseshoe crab) 110–11 Cardiapoda placenta (sea elephant) 305 cardinalfish, bullseye 184 Caretta caretta (loggerhead turtle) 66–67 carotenoid pigments 96 Carta Marina (Magnus) 280–81 cartilaginous fish 84 cartography 280–81 Carukia barnesi (Irukandji jelly) 270 caruncle 200, 201 Cassiopea andromeda (Indo-Pacific upsidedown jellyfish) 108–09 catadromous fish 90 catfish, striped eel 236–37 Caulerpa lentilifera (sea grapes) 186–87 caves 27 cells, sponges 125

Celmins, Vija 64 Ocean Surface 64 cephalic lobes 229 cephalofoils 226 cephalopods colour change 150–51 jet propulsion 208–9 Ceramaster granularis (cushion star) 222 cerata 148, 210, 211 Ceratium hirundinella 259 Cereus pedunculatus (daisy anemone) 30 cetaceans 293, 308 chaetae 201 Chaetoceros debilis 259 Chaetodon lineolatus (lined butterflyfish) 170 Challenger, HMS 153 Champsocephalus gunnari (mackerel icefish) 303 chelae American lobster 213 coconut crab 212 fiddler crab 114, 115 hermit crab 41 horseshoe crab 111 spider decorator crab 156 Chelmon rostratus (copperband butterflyfish) 171, 184 Chelonia mydas (green turtle) 191 chemoautosynthesis 262 chemoreceptor organs 236 Chironex fleckeri (common box jelly) 270 chitin 34, 110, 201 Chlamydomonas reinhardtii 259 Chloeia flava (golden fireworm) 200–01 chlorophyll 63, 186 chloroplasts 136, 186 Chlorurus microrhinos (steephead parrotfish) 183 chromatophores 150, 160 Chromodoris elisabethina (nudibranch) 211 Chrysoara melanaster (northern sea nettle jelly) 271 Chthamalus fragilis (grey acorn barnacle) 38–39 Chthamalus montagui (Montagu’s stellate barnacle) 39 ciguatoxin/ciguatera 142 cilia 144, 215 cirri 200–01, 214, 215 clams giant 146–47 Indo-Pacific blood 81 smooth giant 146–47 Clavelina moluccensis (bluebell tunicate) 105 clavus 278 claws isopods 266 terrapins 121 cleaner fish 154, 155 client fish 154–55 cliffs, bird colonies 54–55 climate currents and 274 ocean 16–17 climate change 16, 288 clingfish, urchin 184 Clio recurva (sea butterfly) 304 Clione limacina (sea angel) 304 clones tunicates 105 turtle seagrass 190, 191

dentine 319 depth, ocean 18–19 Derain, André 52 Dermasterias imbricata (leather star) 222 dermis, cetaceans 308 Desmoceras latidorsatum (fossil) 14–15 detritivores 158–59 detritus 158 Diademichthys lineatus (urchin clingfish) 184 diatoms 258–59, 301 dichotomous branching 130 Didemnum (sea squirt) 124 digestion, anemones 199 digitigrade feet 58 dikes 265 dinoflagellates 136, 142, 258–59 Diodogorgia nodulifera (colourful sea rod) 130–31 Diodon holocanthus (long-spine porcupinefish) 162–63 Diomedea exulans (wandering albatross) 286–87 displacement, water 76, 235 disturbances, ocean 16 dogwhelks 41 dolphins Atlantic spotted 252–53 orca 292–93 dorid nudibranchs 210–11 dorid sea slugs 148 dottyback, magenta 184 dowitchers Asian 92 short-billed 92–93 downwelling 250 dragonfish, smalltooth 283 Dromiidae 157 Dugong dugon (Indo-Pacific dugong) 246–47 Dugong Hunt (Wurrabadalumba) 165 dugong, Indo-Pacific 246–47 dunes 68–69 marram grass 62 nesting birds 74 Dutch Ferry Before a Breeze, A (de Vlieger) 94 Dutch Golden Age 94–95, 281

E

eagles 98 ears, dugong 246 Earth land and water 13 rotation 16, 82, 250, 274, 275 tilt 301 earthquakes coastal erosion 27 and new ocean floor 265 subduction zones 290 and tsunamis 76 echinoderms body support 218 detritivores 158–59 spiny skin 224–25 starfish 222–23 tube feet 220–21 echolocation, dolphins 248 ecosystems 147, 158, 297 ectoparasites 273 ectothermic animals 51 Edmundsella pedata (nudibranch) 210

eels European 46 migration 90 moray 154 pale snipe 47 ribbon moray 168–69 eggs clownfish 167 coral 128, 129, 132 floating 279 gannet 56 giant clam 147 guillemot 55 hooded plover 75 horseshoe crab 111 king penguin 307 marine turtle 66, 67 violet snail 260–61 wandering albatross 287 zooplankton 304 El Niño 16 electric charge 233 electrical fields, sensing 89, 226, 276 electroreceptors 88, 276 elegant unicornfish 172–73 Ellisella ceratophyta (gorgonian sea whip) 135 embayed beaches 68 endothermic animals 276 Eng yprosopon xenandrus (lefteye flounder) 305 Enhydra lutris (sea otter) 244–45 Enophrys diceraus (antlered sculpin) 302–03 enzymes 193, 282 epaulette shark, small 44–45 epaulette soldierfish 140 epidermis cetaceans 308 coral 126 marram grass 62, 63 epithelium, sea fans 130 erosion, coastal 26–27 estuaries 72, 78 changing salinity 120, 121 Étretat. The Cliff of Aval (Boudin) 118 Eudyptes chrysocome (rockhopper penguin) 58–9 Euphausia superba (Antarctic krill) 300–01 euryhaline species 121 eurypterids 110 evaporation 16, 28, 62 evolution convergent 88 horseshoe crabs 110 Lingula brachiopods 111 exoskeletons 266 lobsters and crabs 212 eyes antlered sculpin 302 dugong 247 hammerhead shark 226 isopods 267 king penguin 307 krill 300 painted topshell 35 red-jointed fiddler crab 114 reef stonefish 86, 87 scallop 202 scarlet skunk shrimp 155 southern elephant seal 310 stargazers 233 eyespots common sun star 221 false 151 mid-Atlantic ridge shrimp 262

F

Facelina bostoniensis (nudibranch) 210 fan worm, star 144–45 Fauvism 52–53 feather stars 214–15 feathers blue 160 brown pelican 243 great frigatebird 240 horned puffin 58 osprey 99 roseate spoonbill 97 short-billed dowitcher 93 feeding Antarctic krill 301 barnacles 38, 39 bivalves 81 bubble-net 248 butterflyfish 170 coral 127, 132 dugong 247 echinoderms 221 feather stars 214–15 feeding frenzies 239 fiddler crabs 115 giant clams 147 mobula and manta rays 229 sea fan 130, 131 spoonbills 97 upside-down jellyfish 108 see also filter-feeding; hunting; photosynthesis; suspension feeding feeding-webs, mucus 297 feet clawed 121 osprey 98 plantigrade 58 webbed 58, 121, 245 fighting southern elephant seal 310 walrus 308 filiform fish 46 filter-feeding 215 bivalves 81, 147 blue whale 288 giant clams 147 mobula and manta rays 229 sponges 124 tunicates 105 whale shark 272–73 fins giant ocean sunfish 278, 279 locking mechanism 178 ray-finned fish 178–79 sailfish 284, 285 types of 49 fireworm, golden 200–01 fish antifreeze proteins 302–03 jumping for prey 116 on land 44–45 migration 90–91 ray-finned 178–79 reef 174–75 shapes 46–47 shoals and schools 239 shooting down prey 116 teeth and diet 182 types of fin 49 Fishing Boat at Sea, A (van Gogh) 52

Fjordia chriskaugei (nudibranch) 211 flagella 136, 258, 259 flamingos 96 flippers 313 flotsam 74 flounders lefteye 305 Pacific leopard 46 flowering plants coastal 28–29 seagrasses 190–91 fluorescence 143, 193 flying fish 240 food chains detritivores 158 hydrothermal vents 262 toxins passed along 142 food webs 19, 258, 301, 304 foraminifera 16 Forcipiger flavissimus (yellow longnose butterflyfish) 170 forests, kelp 188–89 Forman, Zaria 64 Maldives No. 11 64–65 fossils 14–15 foraminifera 16 Lingula brachiopods 111 living 110–11 Fragilaria 259 Franklin, Sir John 71 Fratercula corniculata (horned puffin) 54–55 freezing 298 Fregata minor (great frigatebird) 240–41 fresh water 13 physiological changes needed for 90 frigatebird, great 240–41 fringing reef 141 frogfish, warty 46 frond stripes (stems) 24, 25 fruits 191 fungi, lichens 22 fur polar bear 317 sea otter 245 seal 312, 313 walrus 308, 309 fusiform fish 46

G

Gadus morhua (Atlantic cod) 46 Galápagos Islands 50, 51 gamete bundles 128, 129 gannetries 56 gannets 242 northern 56–57 gar, longnose 46 gas bladders 261 gas exchange 62, 221 Gauguin, Paul 52 geology 15 geothermal activity 262 Géricault, Théodore 71 germination 191 Gersemia fruticosa (carnation coral) 134 ghost pipefish, harlequin 176–77 Gigantocypris muelleri (ostracod) 305 gill chambers 45 gill rakers 229 gill slits 85

habitats cliffs 55 coral reefs 140, 154 depth zones 19 intertidal zone 37, 45, 105 kelp forests 189 and light 187 rock pools 48–49

hunting continued southern elephant seal 310 southern stingray 84 spoonbills 97 stargazers 233 Weddell seal 312 white shark 276 hurricanes 206–07 Hydractinia echinata (snail fur) 40 hydrothermal vents 262 hydrozoans 136, 192, 194–95, 270–71 colonial 261 eight-strand jelly 270 golf tee jelly 270 Portuguese man o’war 256, 261, 270 Hypanus americanus (southern stingray) 84–85 Hyperrealism 64–65 hyphae 22

I

Ice Age, last 235 ice crystals 298, 303 ice floes 298 ice-sheets 76, 314 ice-shelves 314–15 icebergs 314–15 calving 76, 314 icefish, mackerel 303 Iceland 265 iguana, marine 50–51 Ilulissat Icefjord 314–15 Impressionism 118–19 Indian Ocean 12 inflation, body 162–63 infrared radiation 262 ink, defensive 148 inland seas 113 interbrachial web, octopus 151 intertidal zone adaptations 30 fish 45 limpets 36–37 plants 102–03 iridescence 160 iridophores 160 Isla Magdalena 68–69 island arcs 290 islands, coral 141 isopod, western Atlantic giant 266–67 Istiophorus platypterus (sailfish) 284–85

J Janthina 260–61 jaws American crocodile 72 brittle star 218 butterflyfish 170, 171 dugong 247 ember parrotfish 183 sea urchins 225 jellyfish 270–71 bioluminescence 192–93 brownbanded moon jelly 271 common box jelly 270 crystal jelly 192–93

jellyfish continued golf tee jelly 270 horned stalked jellyfish 270 Indo-Pacific upside-down 108–09 Irukandji jelly 270 kaleidoscope jellyfish 270 mauve stinger/night light jelly 271 medusae 195 northern sea nettle jelly 271 rhizostome 109 stalked jelly 270 thick-rimmed stalked jellyfish 270 venom 138 winged box jelly 270 Jurassic period 14

K

Kakadu National Park (Australia) 165 keels 285 keelworm 145 kelp, giant 188–89 killer whale see orca kleptoparasites 240, 242 Knossos 181 krill 288 Antarctic 300–1 Kunstformen der Natur (Haeckel) 30, 153, 194–95 Kurodai and Kadai Fish with Bamboo Shoots and Berries (Hiroshige) 217

L

La Niña 16 Labroides dimidatus (bluestreak cleaner wrasse) 155 lachrymal glands 121 lagoons 68, 141 Lamellodysidea chlorea (Indo-Pacific blue sponge) 124 land fish on 44–45, 48 marine turtles 66–67 landmasses, ancient 14, 15 Landseer, Sir Edwin 71 landslides 27, 76, 290 Lane, Fitz Henry 33 lanugo 313 lanternfish 282, 310 Larus atricilla (laughing gull) 242 Larus heermanni (Heermann’s gull) 242 larvae clownfish 167 hydrozoans 195 nudibranch 210 open ocean fish 279 planktonic coral 127, 129 scallop 202 tunicate 105 violet snail 260 zooplankton 304 lateral line 236, 237 lava 265 leaves mangrove 106 marram grass 62 legs, rockhopper penguin 58

index

H

habitats continued rocky coasts 25 salt marshes 102–03 splash zone 22–23 starfish 222 hadal zone 19 Haddon’s carpet anemone 138–39 Haeckel, Ernst 30, 153, 194–95 Haematopus longirostris (pied oystercatcher) 75 haemoglobin 303 hagfish 159 hair follicles, seal whiskers 312 Haliclustus auricula (kaleidoscope jellyfish) 270 Haliclustus salpinx (stalked jelly) 270 halophytes 103 hammerhead sharks 226–27 haptera 25 harems 310 hatchetfish, deepsea 19, 282, 305 hawks 98 headlands 27 heliocentric theory 281 Hemiscyllium ocellatum (small epaulette shark) 44–45 Henricia leviuscula (Pacific blood star) 222 herding 293 hermaphrodites 128, 147 scallops 202 sequential 168 hermit crab, European common 40–41 Hexabranchus sanguineus (nudibranch) 211 hexacorals 131 Hiroshige, Utagawa, Kurodai and Kadai Fish with Bamboo Shoots and Berries 217 history, ocean 14–15, 113, 235 Hokusai, Under the Great Wave off Kanagawa 216–17 holdfasts 24, 25, 189 holoplankton 304–05 Homarus americanus (American lobster) 212–13 Homer, Winslow 33 The Life Boat 33 West Point, Prouts Neck 32–33 horseshoe crabs Atlantic 111 mangrove 110–11 Hudson River School 33 human activity 16 Humboldt current 50 humpback whale 248–49 hunting American crocodile 72 anemones 138, 199 archerfish 116–17 Atlantic spotted dolphin 252 barracudas 230 bioluminescence 282 brown pelican 242 cone snail 201 gannets 56 gorgon star 268 great frigatebird 240 humpback whale 248 king penguin 307 narwhal 319 orca 293 osprey 90–1 reef stonefish 86 sailfish 284, 285 sea otter 245

328 • 329

gills bivalves 80, 81 giant tube worms 263 nudibranchs 210 sea slugs 148, 149 whale sharks 273 glaciers 76, 314 Glaucus atlanticus (nudibranch) 211 global warming carbon sinks 190, 297 hurricanes and typhoons 206 ice-shelves 314 sea-ice 298 sea-level change 235 globiform fish 46 gnathobases 111 gobies 155 glass 184 goblet cells 167 gods and goddesses 196–97 godwit, black-tailed 92 Goniodoris castanea (nudibranch) 210 gonozooids 195 gorgon stars Arctic 268–69 bushy 268 spiny 268 gorgonians 162–63 sea fan 130–31, 134 sea whip 135 gorgonin 130, 131 Gorgonocephalus arcticus (Arctic gorgon star) 268–69 Gorgonocephalus eucnemis (bushy gorgon star) 268 Goyen, Jan van 94 gravitational pull 82 grazing dugong 247 herbivorous snails and limpets 34–35 grease ice 298 Great Barrier Reef 140 great white shark see white shark Greeks, ancient 181, 281 green seaweeds 186 grenadier fish 19 guanine 160 guard hairs 317 guillemots 55 Guinardia striata 258 gular sacs 240 Gulf Stream 274, 275 gulls great black-backed 59 Heermann’s 242 laughing 242 gunnel, crescent 46 Gymnodinium 258 gyres 250, 274

lenticels 107 Lepidochelys olivacea (olive ridley turtle) 67 Lepidophanes guentheri (lanternfish) 283 Lepisosteus osseus (longnose gar) 46 Leptonychotes weddellii 312–13 Liaohe River delta 103 lichens sunburst 22–23 tufted 22 Licmophora flabellata (brackish water diatom) 258–59 Life Boat, The (Homer) 33 life cycle coral (sexual) 129 hydrozoan (sexual) 195 scallop 202 tunicates 105 light depth zones 19 and habitat 187 refraction 242 wavelengths 160, 186–87, 310 see also bioluminescence; photosynthesis Limacia clavigera (nudibranch) 210 Limacina helicina (sea butterfly) 296–97 Limnadromus semipalmatus (Asian dowitcher) 92 Limnodromus griseus (short-billed dowitcher) 92–93 Limosa limosa (black-tailed godwit) 92 limpet, common 34, 36–37 Limulus polyphemus (Atlantic horseshoe crab) 111 Linckia laevigata (blue linckia) 222 Lingula brachiopods 111 lionfish, red 184 Lipophrys pholis (shanny) 48–49 liver, sharks and rays 231 living fossils 110–11 lobster, American 212–13 Lofoten Islands 234–35 loggerhead turtle 66–67 Loligo vulgaris (European squid) 208–09 longshore drift 68 Lophelia pertusa (cold-water coral) 19 Lucernaria quadricornis (horned stalk jellyfish) 270 luciferase 282 luciferin 282 lugworms 201 Luidia senegalensis (nine-armed star) 222 Luminist style 33 lures 233 Lutjanus apodus (schoolmaster snapper) 184 Lutjanus campechanus (northern red snapper) 182 Lybia (pom-pom crab) 157 Lysmata amboinensis (scarlet skunk shrimp) 154–55

M

mackerel 19, 56, 226 Macrocystis pyrifera (giant kelp) 188–89 magma 265, 290 Magnus, Olaus 280, 281 Malaclemys terrapin (diamondback terrapin) 120–21 Maldives No. 11 (Forman) 64–65 manatees, Atlantic 247

mangroves 100, 106–07 colonized roots 104–05, 107 red 106–07 mannitol 24 mantle cuttlefish 204 Earth’s 265 nudibranchs 210 squid 209 map-making 280–81 marine turtles green 191 loggerhead 66–67 olive ridley 67 marlin 285 marram grasses 62–63 Marrus orthocanna (siphonophore) 256 mating bioluminescence 282 butterflyfish 170 fiddler crab 114, 115 gannet 56 great frigatebird 240 horseshoe crab 111 humpback whale 248 king penguin 307 orca 293 sea otter 245 southern elephant seal 310 wandering albatross 286, 287 Matisse, Henri 52 Maupassant, Guy de 118 Maury, Matthew Fontaine 153 Mazu/Tianfei 196, 197 Mediterranean Sea 12, 113, 181 medusae cubozoa 270 hydrozoans 195, 270, 271 jellyfish 271 Megaptera navaeangliae (humpback whale) 248–49 Meiacanthus grammistes 175 Melicertum octocostatum (eight-strand jelly) 270 meroplankton 304–05 mesoglea 199 Mesonychoteuthis hamiltoni (colossal squid) 267 mesophyll 63 mesophytes 103 Metasepia pfefferi (flamboyant cuttlefish) 204–05 Metridium senile (plumose anemone) 30 mid-ocean ridges 113, 235, 265, 290 midnight zone 19 migration fish 90–91 humpback whale 248 sardine run 238–39 Millepora (fire hydrocorals) 136–37 mimicry 176–77 minerals coral reefs 127 dissolution from land 113 hydrothermal vents 262 Minoan civilization 181 Minuca minax (red-jointed fiddler crab) 114–15 Mirounga leonina (southern elephant seal) 310–11 Mola mola (giant ocean sunfish) 278–79 molluscs bivalves 80–81, 202 cephalopods 208–9

molluscs continued herbivorous snails and limpets 34–35 nutrition 136 soft-bodied 148–49 Monet, Claude 118 Impression, Sunrise 118–19 Monodon monoceros (narwhal) 318–19 Moon and coral spawning 128, 129 and tides 82 and turtle hatchlings 66 moray, ribbon 168–69 Morus bassanus (northern gannet) 56–57 mosaics 180–81 moulting lobsters 212 seals 310, 312 mouths brittle stars 218 feather stars 214, 215 reef stonefish 86, 87 rhizostome jellyfish 109 scalloped hammerhead shark 226 stingrays 84, 85 movement American crocodile 72 brittle stars 218 cephalopods 208–09 echinoderms 220–11 epaulette shark 44 fish shapes 46–47 gorgon stars 268 jellyfish 109 mobula and manta rays 229 penguins 59 plankton 279 scallops 202 sea butterfly 297 starfish 218, 268 swim bladders 231 zooplankton 304 mucopolysaccharides 25 mucus anemones 198 brittle stars 218 clownfish 167 limpets 37 mandarinfish 160 painted topshell 34, 35 sea butterfly 297 secreting 167 violet snail 260, 261 mud, feeding in 92 mudflats 45, 78, 92, 115 mudskippers 45 Atlantic 45 Mundy, Peter 94 muscular foot bivalves 80 limpets 37 nudibranchs 211 painted topshell 34, 35 scallops 202 sea butterfly 297 violet snail 261 mutual fencing 56 Myripristis kuntee (epaulette soldierfish) 140 mythology Asian 196–97 Graeco-Roman 181 Scandinavian 281

N

Najombolmi 164–65 narwhal 318–19 Naso elegans (elegant unicornfish) 172–73 nautilus 205 neap tides 82 nectosome 256 nematocysts 138, 148, 167, 193, 210, 270 Nembrotha kubaryana (variable neon sea slug) 148–49, 210 Nemichthys scolopaceus (pale snipe eel) 47 Neoerdina cumingi (Cuming’s sea star) 222 nests American crocodile 72 cliff nesting 54–55 gannets 56 ground-nesting birds 75 hooded plover 74, 75 marine turtles 66, 67 wandering albatross 287 Noctiluca scintillans 258 Northwest Passage 71 Norwegian-Greenland Sea 250 nostrils catfish 237 walrus 309 notochord 105 Nova totius terrarum orbis tabula (Blaeu) 281 nudibranchs 153, 210–11 Numenius madagascarensis (eastern curlew) 92

O

oaten pipes 195 Obelia 195 Ocean Life (Sommerville) 152–53 Ocean Surface (Celmins) 64 oceanic crust 265, 290 oceanic plates 290 octocorals 130, 131, 134 octopus 205, 208 coconut 40 colour change 150–51 day 150–51 wonderpus 304 Octopus cyanea (day octopus) 150–51 Odobenus rosmarus (walrus) 308–09 odontophore 34 olive ridley turtle 67 Oncorhynchus gorbuscha (pink salmon) 90–91 open ocean 254–93 operculum 34, 144 Ophiothrix fragilis (European common brittle star) 218–19 oral arms 108, 109 oral disc 138, 139 orca 292–93, 301 Orcinus orca (orca) 292–93 osculum 124, 125 osmosis 28, 102, 103 osprey 98–99 ossicles 218 ostium 124, 125 Ostorhinchus fleurieu (bullseye cardinalfish) 184 ostracod 305 otter, sea 244–45 oystercatcher, pied 75 oysters 147

P

Pristis pectinata (smalltooth sawfish) 88–89 proboscis cone snail 201 elephant seal 310 protandry 168 protists 189 protogyny 168 Pseudanthias ignitus (flame anthius) 184 Pseudocolochirus violaceus (sea apple) 158 pseudopaxillae 222 Pteraeolidia ianthina (nudibranch) 211 Pterois volitans (red lionfish) 184 pteropods 297 Ptolemy 281 Ptychodera flava 304 pufferfish 162, 279 puffin, horned 54–55 pupils king penguin 307 octopus 151 Pycnopodia helianthoides (sunflower sea star) 223

R

S

sabelids 145 Saccharina latissima (sugar kelp) 24–25 sagittiform fish 46 sailfish 284–85 St Elmo’s fire 197 salmon body changes 91 pink 90–91 salt cycle 113 salt marshes 100, 102–03 salt tolerance adapting to changing salinity 120–21 American crocodile 72 conformers and regulators 120 flowering plants 28 halophytes 103 intertidal plants 102 mangroves 106 nasal salt glands 51 wandering albatross 287 salt water 112–13 volume on Earth 13 sand beaches and dunes 68–69 excreting 183 sand spits 68 sandpipers East-Asian 92 spoon-billed 92 Terek 92 Sarcophyton (leather coral) 132–33 Sardina pilchardus (European pilchard) 238–39 Sargocentron spiniferum (sabre squirrelfish) 175 satellite images 12 sawfish, smalltooth 88–89 sawsharks 88 scales bladed fish 172–73 light-scattering 239 scallop, bay 202–03 Scarus flavipectoralis (yellow-finned parrotfish) 182–83 Scarus rubroviolaceus (ember parrotfish) 182–83 Scarus vetula (queen parrotfish) 182 scavenging 159, 267

index

radioles 144 radula 34, 35, 201 rafts bubble 260–61 sea otters 245 rainfall 15, 16, 206 Ramalina siliquosa (sea ivory) 22 Ramayana 197 ram’s horn 205 ramuli 187 raptors 98–99 ray-finned fish 178–79 rays buoyancy 231 manta 229 mobula 228–29 sawfish 88–89 senses 88, 89 razorbill 55 recycling 158–59 Red Sea 15, 113 red seaweeds 186, 187 red tides 258 reef building 127 Reeves, John 153 refraction 117, 242 remora 273 respiration coral 135, 136 echinoderms 221 fish on land 45 jellyfish and hydrozoans 271 marram grass 62 shannies 49 star fan 145 Rhincodon typus (whale shark) 272–73 Rhinomuraena quaesita (ribbon moray) 168–69 rhinophores 148, 149, 210 rhizines 22 rhizomes 62, 190 Rhizophora mangle (red mangrove) 106–07 Rhizophora mangroves 107 rhizostome jellyfish 109 rhopalia 270 Riftia pachyptila (giant tube worm) 263

Rimicaris exoculata (mid-Atlantic ridge shrimp) 262–63 Ring of Fire 290 rip-currents 27, 68 rivers minerals carried by 113 tidal 72 rock pools, territories 48–49 rock type and coastal erosion 27 and sand colour 68 rocky coasts 20–59 Romans 180–81 Romantic movement 33, 71 rookeries, turtle 67 roots 28 mangroves 104–07 marram grasses 62 rorquals 288 Rosalina globularis (living foraminifera) 16

330 • 331

Pachycerianthus multiplicatus (firework tube anemone) 198–99 Pachystomias microdon (smalltooth dragonfish) 283 Pacific Ocean 12, 13, 15 El Niño effect 16 subduction zones 290 waves 43 Paestum 181 Pagurus bernardus (European common hermit crab) 40–41 painted topshell 34–35 palaeontology 15 palatal fold 94 palatal valve 94 palps 81, 144, 145, 200 pancake ice 298 Pandion haliaetus (osprey) 98–99 papilla, cuttlefish 204 parapodia 200, 297 parasites 154, 155, 167 parrotfish ember 182–83 excavating 183 queen 182 steephead 183 yellow-finned 182–83 passive ram filtration 273 Patella vulgata (common limpet) 34, 36–37 paws polar bear 317 sea otter 245 pebble beaches 68 pedalia 270 pedicellaria 225 Pelagia noctiluca (mauve stinger/night light jelly) 271 Pelecanus occidentalis (brown pelican) 242–43 pelican, brown 242–43 Pelurosigma angulatum 259 penguins 301 emperor 307 king 306–07, 311 rockhopper 58–59 Pentaceraster alveolatus (honeycomb cushion star) 223 Pentaceraster cumingi (Panamic cushion star) 222 Periophthalmus barbarus (Atlantic mudskipper) 45 periwinkles 37–38, 41 Pholis laeta (crescent gunnel) 46 photophores 192, 193, 282, 283 Photorealism 64–65 photosynthesis algae on coral 126, 132, 135, 136 algae on jellyfish 108, 138 algae in lichens 22 algae on zoanthids 142 giant kelp 189 marram grass 62, 63 phytoplankton 258, 301 seagrasses 190 seaweeds 24, 25, 186–87 zooxanthellae 136 phycobiliproteins 187 Physalia physalis (Portuguese man o’war) 256, 261, 270

phytoplankton 19, 250, 258–59, 288, 301, 304 Pictichromis poryphyrea (Magenta dottyback) 184 pigment blue 160–61 colour change 150–51 seaweeds 186 zoanthids 142 pilchard, European 238–39 pillow lava 265 pincers see chelae pinnipeds 308 pinnules 215 pipefish, harlequin ghost 172–73 pits, sensory 88, 89 plankton 132, 135 giant 278–79 Planktoniella sol 258 plantigrade feet 58 Platalea ajaja (roseate spoonbill) 96–97 plate boundaries 265, 290 pleuston 261 Pliny the Elder 181 Plotosus lineatus (striped eel catfish) 236–37 plover, hooded 74–75 plumage see feathers plunge diving 242 pneumatocysts 189 pneumatophores 107, 256 pocket beaches 68 pods dolphins 252 narwhal 319 orca 293 polar bear 316–17 polar ice caps 235 polar oceans 294–319 sea-ice 298–99 polar regions, light 301 pollen 191 pollination 28 Polycera quadrilineata (nudibranch) 211 polyps anemones 138 coral 127, 128, 132, 134–35, 140 cubozoa 270 hydrozoans 195, 271 jellyfish 271 octocorals 130, 131 siphonophores 256 tentacled 105 zoanthids 142 Pomacanthus imperator (emperor angelfish) 46 Pomatostegus stellatus (star fan worm) 144–45 Pompeii 181 Pop Art 64 Porcellanaster ceruleus (deepsea star) 223 porcupinefish 162 long-spined 162–63 pores, pressure sensitive 239 porphyrins 35 Port-Miou (Braque) 52–53 Portuguese man o’war 256, 261, 270 Post-impressionists 52 posture, penguins 59 pouches brown pelican 242 king penguin 307 sea otter 245 Premnas biaculeatus (maroon clownfish) 166–67 pressure changes 236, 237

schools herding 284, 285 mobula rays 229 sardines 238–39 scalloped hammerhead sharks 226–77 Schussele, Christian 152–53 scorpion, giant water 110 scorpionfish 86 scrapes 75 sculpin, antlered 302–03 scyphozoa 271 sea angel 304 sea apple 158 sea blites Australian 102 Eurasian 102–03 sea butterfly 296–97, 304 sea cucumber, thorny 158–59 sea elephant 305 sea fan 130–31, 134 sea grapes 186–87 sea hare 148 sea-ice 298–99 sea ivory 22 sea level, changing 234–35 sea lions 189, 245, 293, 308 sea otter 244–45 sea rod, colourful 130–31 sea slugs 148 variable neon 148–49 sea snakes 86 sea squirts 124, 148, 149 sea stacks 27 sea stars Cuming’s 222 paddle-spined 222 sunflower 223 sea thrift 28–29 sea urchins 221 collector 224–25 purple 25 seagrass, turtle 190–91 seals 301 southern elephant 310–11 Weddell 312–13 seascapes 71 seaweed food sources in 74, 75 photosynthesis 186–87 pigments 186–87 rocky coasts 24–25 sediment beaches 68 coastal erosion 27 colliding plates 290 hunting in 84, 85 living in 80–81 seeds 191 Semibalanus balanoides (acorn barnacle) 39 sensory data catfish 236–37 dragonfish 283 rhinophores 149 tusks 319 whiskers 312 Sepia elegans (elegant cuttlefish) 205 sequential hermaphrodites 168 serpulids 145 setae 39 sex changes clownfish 167 fish 168

sex changes continued parrotfish 183 ribbon moray 168–69 sexual dimorphism 115, 310 sexual reproduction coral 128–29 scallops 202 turtle seagrass 191 see also mating shanny 48–49 shape-changing, octopus 151 sharks basking 273 buoyancy 231 hammerhead 88 megamouth 273 scalloped hammerhead 226–27 scavenging 159 senses 88, 89 small epaulette 44–45 swell 162 whale 272–73 white 276–77 shells acorn barnacles 36 ammonites 14 bivalves 80, 81 cephalopods 205 coconut octopus 40 fossil 111 giant clams 147 hermit crab 40–41 painted topshell 35 sea butterfly 297 and sea temperature 16 violet snail 261 waves and shell shape 37 shipbuilding 94 shoals 239 hunting in 117 shockwaves 76 shorebirds 74–75, 92–93 shoreline coastal erosion 26–27 sea-level change 234–35 shrimps mid-Atlantic ridge 262–63 scarlet skunk 154–55 Silfra Canyon 264–65 silicon 258 Sinularia flexibilis (spaghetti finger leather coral) 135 siphonophores 271 colonial structure 256 cup-bearing 256–57 siphons bivalves 81 cephalopods 208, 209 cone snails 201 siphosome 256 sirenians 247 skates 88, 229 skeletons crabs 212 fire hydrocorals 136 great black-backed gull 59 great frigatebird 240 lobsters 212 rockhopper penguin 59 sea fan 130–31 stony corals 127

skin Atlantic spotted dolphin 252 brittle stars 218 cetaceans 308 diamondback terrapin 121 echinoderms 224–95 giant ocean sunfish 279 marine iguana 50–51 polar bear 317 reef stonefish 86 sawfish 89 starfish 218 walrus 308 slime sea slugs 148 turtle seagrass 191 smell, sense of rays and skates 88 salmon 91 sea otter 245 sharks 88, 226, 276 walrus 309 smooth giant clam 146–47 snails cone 201 painted topshell 34–35 sea butterfly 296–97 violet 260–61 snappers northern red 182 schoolmaster 184 snouts epaulette shark 44 harlequin ghost pipefish 177 ribbon moray 168, 169 sailfish 285 sawfish 88–9 solenia 130, 132 Solenostomus paradoxus (harlequin ghost pipefish) 176–77 Sommerville, James M. 152–53 sound waves 236 Southern Ocean 12, 43 spawning coral 128–29, 132 salmon 90–91 speed billfish 285 northern gannet 56 orca 293 wandering albatross 287 white shark 276 Sphyraena putnamae (chevron barracuda) 230–1 Sphyrna lewini (scalloped hammerhead shark) 226–27 spicules 125 spines echinoderms 224–25 elegant unicornfish 172–73 pufferfish, balloonfish, and porcupinefish 162–63 starfish 222, 223 spiracles 85 Spirobranchus lamarki (keelworm) 145 splash zone 22–23 sponges 124–25 calcareous 125 crab decór 156, 157 demosponges 125 glass 125 Indo-Pacific blue 124 nutrition 136

spoonbill, roseate 96–97 spring tides 82 squalene 231 squid 19, 205, 208, 301 colossal 267 European 208–09 giant 267 glass 305 squirrelfish, sabre 175 starfish 218, 221, 222–23, 268 crown-of-thorns star 223 deepsea star 223 leather star 222 nine-armed star 222 see also brittle stars; gorgon stars; sea stars; cushion stars stargazers 86 Atlantic 233 whitemargin 232–33 staurozoa 270 Stenella frontalis (Atlantic spotted dolphin) 252–53 stenohaline species 121 Stichodactyla haddoni (Haddon’s carpet anemone) 138–39 stingers, storing 148 stingrays, southern 84–85 stings see venom stomata, marram grass 62, 63 stonefish, reef 86–87 Storck, Abraham 94–95 storms coastal erosion 27 hurricanes and typhoons 206–07 waves 43 striped fangblenny 175 Suaeda australis (Australian sea-blite) 102 Suaeda salsa (Eurasian sea-blite) 102–03 subduction zones 290 submarine slides 76 sugar kelp 24–25 sugars 24, 138, 167, 186–87, 262 Sulculeolaria biloba (cup-bearing siphonophore) 256–57 sulphur 159 Sun gravitational pull and tides 82 heat from 16 sun star, common 220–21, 222 sunfish, giant ocean 278–79 sunlit zone 19 supercell thunderstorms 16 Supergorgia (gorgonian sea fan) 134 surf 43 surface currents 16, 274 surgeonfish elegant unicornfish 172–73 elongate 175 suspension feeding 158, 214–15 swell 43 swim bladders 230–31 Swima bombiviridis (green bomber worm) 221 swimming bells 256 swordfish 285 symbiotic relationships cleaner fish 154, 155 tube worms 263 Synanceia verrucosa (reef stonefish) 86–87 Synchiropus splendidus (small mandarinfish) 160–61

T

ukiyo-e 216–17 Under the Great Wave off Kanagawa (Hokusai) 216–17 underfur 245, 317 unicornfish 172 uplift 27, 235 upwelling currents 250 volcanic material 265 Uranoscopus scaber (Atlantic stargazer) 233 Uranoscopus sulphureus (whitemargin stargazer) 232–33 urchins see sea urchins uropods 41 Urticina felina (dahlia anemone) 138 Utica 180–81

V

van Gogh, Vincent 52, 217 A Fishing Boat at Sea 52 Varuna 197 Velde, Willem van de 94 Velella velella (by-the-wind sailor) 261

W

walrus 308–09 waste recycling 147 water freezing 298 gulping 162 plants 103 volume in oceans 13 water purification 147 water vapour 15, 206 water-vascular system 208, 218, 221, 223 wave-washing 293 waves 12, 42–43 beaches 68 and coastal erosion 27 and shell shape 37 tides 82–83 tsunamis 76–77 weather 16 West Point, Prouts Neck (Homer) 32–33 whales baleen 273, 288, 301 blue 267, 288–89 carcasses 159 humpback 248–49 killer see orca narwhal 318–19 toothed 288 whiskers dugong 246 sea otter 245 seals 312, 313 walrus 308 wind and climate 16 and currents 274 dunes 68 hurricanes and typhoons 206–07 and upwelling and downwelling 250 and waves 43 wind tolerance, marram grass 62

winged box jelly 270 wings great frigatebird 240 osprey 98 rockhopper penguin 59 sea butterfly 297 wandering albatross 287 woodcuts, Japanese 216–17 woodlice 266, 267 worms annelid (segmented) 145, 200–01 as detritivores 159 fan 144–45 giant tube 263 golden fireworm 200–01 green bomber 201 wrasse 155 bluestreak cleaner 155 sex change 168 see also parrotfish Wunderpus photogenicus (wonderpus octopus) 304 Wurrabadalumba, Jabbargwa “Kneepad”, Dugong Hunt 165

X, Y, Z

Xanthoria parietina (sunburst lichen) 22–23 Xenus cinereus (Terek sandpiper) 92 Xiphasia setifer (hair-tail blenny) 46 yellow-finned parrotfish 182–83 Yolŋu people 165 young American crocodile 72 Atlantic spotted dolphin 252 black-tailed godwit 92 clownfish 167 giant ocean sunfish 279 hammerhead shark 226 humpback whale 248 king penguin 307 loggerhead turtle 66–67 orcas 293 razorbill 55 spoonbill 97 Weddell seal 313 white shark 276 see also larvae Zheng He 197 zoanthids 142–43 zones, depth 19 zooids 256 Zoological Society of London 153 zooplankton 304–05 reef associated 171, 175 zooxanthellae 126, 135, 136, 147, 167

index

U

veligers 202 venom anemones 138, 167, 198 annelids 201 cnidarians 138 cone snails 201 coral 132 cubozoa 270 fire hydrocorals 136 hydrozoans 261 jellyfish 193, 271 pufferfish, balloonfish, and porcupinefish 162 reef stonefish 86 sea slugs 148–49 sea urchins 225 stingrays 84 zoanthids 142 vibrations 236 Vlieger, Simon de, A Dutch Ferry Before a Breeze 94 vocalization Atlantic spotted dolphin 252 humpback whale 248 orca 293 volcanic activity 76, 113, 141, 265, 290

332 • 333

tactile receptors 213 tactolocation 97 taeniform fish 46 tails giant ocean sunfish 278, 279 sailfish 285 stingrays 84 talons 98 tang, lipstick 172–73 tap roots 28 taste buds 236 Taxotes jaculatrix (banded archerfish) 116–17 tears, diamondback terrapin 121 tectonic activity 27, 141, 235, 265, 290 teeth American crocodile 72 common limpet 34 and diet 182 epaulette shark 44 marine iguana 50 narwhal 319 retractable 276 sawfish 88, 89 scalloped hammerhead shark 226 whale shark 273 white shark 276 telsons hermit crab 41 horseshoe crab 110 temperature coral reefs 136, 140 depth zones 19 giant kelp 189 and hurricanes/typhoons 206 and sex determination 67 tendrils, gorgon stars 268 tentacles anemones 138, 167, 198–99 coral 19, 127, 129, 132 hydrozoans 195, 261, 270 jellyfish 193, 271 molluscs 35 nudibranchs 210 sea apple 158 sea cucumber 159 siphonophores 256 squid 208, 209, 267 zoanthids 142, 143 Tergillarca granosa (Indo-Pacific blood clam) 81 terrapin, diamondback 120–21 test 208 Thalassia testudinum (turtle seagrass) 190–91 Thinornis cucullatus (hooded plover) 74–75 thorny sea cucumber 158–59 thunderstorms 206 tidal currents 27 tidal pools 30 tidal range 82 tides 82–83 coastal erosion 27 iceberg formation 314 toes osprey 98, 99 rockhopper penguin 58 Tomopteris (Johnstonella) helgolandica (bristleworm) 305 tools, sea otter 245 touch, sense of sea otter 245

touch, sense of continued seals 312 walrus 308 toxins, bioaccumulation of 142 trade, Dutch Golden Age 94 trenches, ocean 290 trevally, bluefin 175 Triactis anemones 157 Triceratium favus 258 Tridacna derasa (smooth giant clam) 146–47 Tridacna gigas (giant clam) 146–47 triggerfish clown 178–79 orange-lined 184 Tripneustes gratilla (collector urchin) 224–25 Tripos lunula 259 tropics 16 tsunamis 76–77, 290 Tubastraea coccinea (tube coral) 135 tube feet 215 brittle stars 218 echinoderms 220–21 sea urchins 208 starfish 218, 222 tubercules 208 tubes, fan worms 145 Tubipora musica (organ-pipe coral) 131 Tubularia indivisa (oaten pipes) 195 tubules 319 tunicates 104–05 bluebell 105 life cycle 105 Turner, J.M.W. 71 The Slave Ship 70–71 turnstone, ruddy 92 turtles see marine turtles tusks narwhal 319 walrus 308 twilight zone 19 typhoons 206–07

acknowledgments DK would like to thank: Derek Harvey for helping to plan the contents, advice on photoshoots, and for his comments on the text and images; Rob Houston for helping to plan the contents list; Trudy Brannan and Colin Ziegler at the Natural History Museum, London, for their comments on the text; Barry Allday, Ping Low, Peter Mundy, and James Nutt at the Goldfish Bowl, Oxford, for their help with photoshoots; Steve Crozier for Photoshop retouching; Rizwan Mohd for work on high-resolution images; Katie John for proof-reading; and Helen Peters for compling the index. DK would also like to thank: Senior Jacket Designer: Suhita Dharamjit Senior DTP Designer: Harish Aggarwal Senior DTP Designer: Harish Aggarwal Jackets Editorial Coordinator: Priyanka Sharma Senior Jacket Designer: Suhita Dharamjit Managing Jackets Editor: Saloni Singh

The publisher would like to thank the following for their kind permission to reproduce their photographs: (Key: a-above; b-below/bottom; c-centre; f-far; l-left; r-right; t-top) 1 Nat Geo Image Collection: David Liittschwager. 2-3 Alamy Stock Photo: National Geographic Image Collection / Andy Mann. 4-5 Science Photo Library: Alexander Semenov. 6 Nat Geo Image Collection: David Liittschwager. 8-9 naturepl.com: Ralph Pace. 10-11 Dreamstime.com: Valiva. 12-13 Warren Keelan Photography. 12 123RF.com: Leonello Calvetti (cra). 14-15 Science Photo Library: Pascal Goetgheluck. 15 Science Photo Library: George Bernard (tr). 16 Alamy Stock Photo: Scenics & Science (tl). 16-17 iStockphoto.com: Petesphotography / E+. 18 Alamy Stock Photo: TommoT. 19 NOAA: Lophelia II 2009: Deepwater Coral Expedition: Reefs, Rigs, and Wrecks (bc). 20-21 Dreamstime.com: Andrii Oliinyk. 22 Alamy Stock Photo: Jonathan Need (tl). 22-23 Getty Images: VW Pics / Universal Images Group. 24-25 Alamy Stock Photo: Jennifer Booher. 25 Alamy Stock Photo: Mark Conlin (tc). 26-27 Getty Images: Warren Ishii / 500px. 28 SuperStock: Silvia Reiche / Minden Pictures (bc). 29 Alamy Stock Photo: Florilegius. 30 Alamy Stock Photo: Scott Camazine (bc). iStockphoto.com: AlbyDeTweede (tc). 30-31 naturepl.com: Alex Hyde. 32-33 Alamy Stock Photo: Artokoloro. 33 Smithsonian Design Museum: Cooper Hewitt Collection / Donated By Charles Savage Homer, Jr. (tr). 34 naturepl.com: Jason Smalley (tr). Ian Frank Smith | ‘Morddyn’: (bl, bc, br). 35 Ian Frank Smith | ‘Morddyn’. 36-37 © Pixelda Software Limited. 37 [email protected]: (tr). 38-39 Igor Siwanowicz. 39 SuperStock: Nico van Kappel / Minden Pictures (cb). 40-41 FLPA: Ingo Arndt / Minden Pictures. 40 Alamy Stock Photo: Nature Picture

Library / Constantinos Petrinos (tl, cla, cl). 42-43 Alamy Stock Photo: Media Drum World. 46 Alamy Stock Photo: National Geographic Image Collection / Joel Sartore (br); WaterFrame (cla); Nature Picture Library / Constantinos Petrinos (bl). SuperStock: Wil Meinderts / Minden Pictures (tl). 47 naturepl. com: David Shale. 48-49 Tim Hunt Photography. 48 Alamy Stock Photo: Nature Picture Library / Alex Hyde (bl). 50-51 Alamy Stock Photo: Bill Attwell. 50 Nat Geo Image Collection: Greg Lecoeur (tr). 52-53 Alamy Stock Photo: Peter Horree. 52 Saint Louis Art Museum: Gift of Mr. and Mrs. Joseph Pulitzer Jr. (tl). 54 Kirt Edblom. 55 Alamy Stock Photo: Mike Read (tl). Image from the Biodiversity Heritage Library: British Oology (tr). © Jenny E. Ross / www.jennyross. com.: (br). 56 Nat Geo Image Collection: Klaus Nigge (bl). 56-57 Rebecca Nason Photography. 58-59 Nat Geo Image Collection: Thomas P. Peschak. 58 Alamy Stock Photo: Arco Images GmbH / C. Kutschenreiter (tr). 60-61 Shutterstock.com: Andrey Oleynik. 62 Alamy Stock Photo: Blickwinkel / H. Schulz (tl). 62-63 Science Photo Library: Gerd Guenther. 64-65 Courtesy of the artist Zaria Forman. 64 Bridgeman Images: Mr. and Mrs. Jake L. Hamon Fund / Ocean Surface (First State), 1983, Drypoint on Rives BFK paper, Image size: 19.8 x 25 cm, Paper size: 66 x 50.8 cm, Edition of 75, Printed by Doris Simmelink, Published by Gemini G.E.L., Los Angeles, CA. / Vija Celmins (tc). 66-67 Getty Images: Cyndi Monaghan / Moment Open. 67 Dreamstime.com: Mirror Images (cr). 68-69 Nat Geo Image Collection: George Steinmetz. 70-71 Alamy Stock Photo: Art Heritage. 71 Alamy Stock Photo: Classicpaintings (tr). 72-73 Antonio Pastrana. 74-75 Alamy Stock Photo: Phototrip. 75 Simon Grove: (tl). Image from the Biodiversity Heritage Library: The Birds of Australia By John Gould (cra). 76-77 Getty Images: The AGE / Fairfax

Media. 78-79 Alamy Stock Photo: World History Archive. 80-81 Dreamstime.com: Yodsawaj Suriyasirisin. 80 Alamy Stock Photo: Natural Visions / Heather Angel (tr). 82-83 Fortunato Gatto / Fortunato Photography. 84-85 Andy Deitsch Photography. 84 Andy Deitsch Photography: (cl); naturepl.com: Shane Gross (tr). 85 Andy Deitsch Photography: (tr). 86 Alamy Stock Photo: Helmut Corneli (bc). 86-87 Wesley Jay Oosthuizen. 88-89 Science Photo Library: Sandra J. Raredon, National Museum Of Natural History, Smithsonian Institution. 88 Rex by Shutterstock: Rob Griffith / AP (clb). 90 SuperStock: Jelger Herder / Buiten-beeld / Minden Pictures (cra). 90-91 Alamy Stock Photo: Design Pics Inc. 92-93 Nat Geo Image Collection: Joel Sartore - National Geographic Photo Ark. 92 Alamy Stock Photo: Buiten-Beeld / Astrid Kant (clb). 94 Alamy Stock Photo: The Picture Art Collection (tl). 94-95 Amsterdam Museum: SA 5611. 9697 Pedro Jarque Krebs. 97 Alamy Stock Photo: Harry Collins (tr). 98 Taiwanese Photographer Wilson Chen. 99 Taiwanese Photographer Wilson Chen. 100-101 iStockphoto.com: Ilbusca / Digitalvision Vectors. 102 Black Diamond Images: (tr). 102-103 Ke Guo. 104-105 Phil’s 1stPix. 105 SuperStock: Christian Ziegler / Minden Pictures (tr). 106 Rex by Shutterstock: Auscape / UIG (tr). 106-107 SuperStock: Kevin Schafer / Minden Pictures. 108-109 Nat Geo Image Collection: David Liittschwager. 109 Nat Geo Image Collection: David Liittschwager (tr). 111 Alamy Stock Photo: Florilegius (br). Ariane Müller: (cb). 112-113 Getty Images: Ruslan Kalnitsky / 500px. 114 iStockphoto.com: Mccluremr (t); Mccluremr (b). 115 iStockphoto.com: Mccluremr (bc). 116 naturepl.com: Kim Taylor (tr). 116-117 Dreamstime.com: Marcel De Grijs (ca). 118-119 Alamy Stock Photo: Heritage Image Partnership Ltd. 118 Alamy Stock Photo: Peter Horree (tl). 120-121 Getty Images:

Science Photo Library: Alexander Semenov (t). 194 Kunstformen der Natur by Ernst Haeckel. 195 Science Photo Library: Alexander Semenov (bc); Alexander Semenov (br). 196-197 Rijksmuseum, Amsterdam: Gift of Mr and Mrs Dissevelt-van Vloten. 197 Alamy Stock Photo: The History Collection (tr). 199 Alamy Stock Photo: Nature Picture Library / Richard Robinson (tr). 200-201 BioQuest Studios. 201 Dr. Karen Osborn: (tr). 202-203 David Moynahan. 202 Alamy Stock Photo: David Fleetham (c). 204 Ramiro Gonzalez: (bc). 204-205 Todd Aki / https://www.flickr. com/photos/90966819@N00/ albums. 205 Alamy Stock Photo: StellaPhotography (tc). Science Photo Library: Power And Syred (tr). 206-207 ESA: NASA / A.Gerst. 208-209 Science Photo Library: Alexander Semenov (t); Alexander Semenov (c). 208 Getty Images: Wild Horizon / Universal Images Group (br). 210 Alamy Stock Photo: Stocktrek Images, Inc. / Ethan Daniels (fbr). naturepl.com: Alex Mustard (c, cr, fcr, bc, br). 211 Alamy Stock Photo: Nature Picture Library / Franco Banfi (cr). Getty Images: Antonio Camacho / Moment Open (cl). naturepl.com: Franco Banfi (bc); Alex Mustard (c); Solvin Zankl (bl); Norbert Wu (br). Alexander Semenov: (t). 212 Alamy Stock Photo: Blickwinkel (tl). 212-213 Getty Images: Maarten Wouters / Stone. 215 Alamy Stock Photo: Brandon Cole Marine Photography (bc). 216-217 Getty Images: Fine Art / Corbis Historical. 217 Alamy Stock Photo: Antiquarian Images (tc). 220-221 Alexander Semenov. 221 naturepl.com: Sue Daly (tc). 222 Alamy Stock Photo: Pulsar Imagens (tr); WaterFrame (cr). iStockphoto. com: Searsie (bc). Museums Victoria: Chris Rowley / CC BY 4.0 (cl). Nat Geo Image Collection: Joel Sartore - National Geographic Photo Ark (br). naturepl.com: Sue Daly (tl); Georgette Douwma (tc); Visuals Unlimited (c); Lynn M. Stone (bl). 223 iStockphoto.com: Tae208 (tl). naturepl.com: Georgette

Douwma (br); Norbert Wu (cl); David Shale (bl). 224 Alamy Stock Photo: Panther Media GmbH / Jolanta Wójcicka (bc). 226-227 Edwar Herreno. 226 James Ferrara: (b). 228-229 Jorge Cervera Hauser / Pelagic Fleet. 229 Dreamstime. com: Sergey Uryadnikov (tc). 230-231 SuperStock: Minden Pictures. 232 Science Photo Library: Alex Mustard / Nature Picture Library. 233 Alamy Stock Photo: Imagebroker (br); Andrey Nekrasov (cb). naturepl. com: Visuals Unlimited (cra). 234-235 Getty Images: Yuichi Sahacha / 500Px Plus. 238-239 Davide Lopresti. 239 iStockphoto.com: Clintscholz / E+ (tr). 240-241 Malcolm Thornton Photography. 240 Getty Images: Wei Hao Ho / Moment (clb). 242 National Audubon Society: (bc). naturepl.com: Alan Murphy / BIA (t); Tui De Roy (br). 243 Alamy Stock Photo: Paul Barnes. 244-245 Alamy Stock Photo: Design Pics Inc / Tom Soucek. 245 Science Photo Library: Thomas & Pat Leeson (tr). 246-247 Sheila Smart Photography. 247 iStockphoto. com: Cinoby / E+ (bc). 248-249 Gabriel Barathieu: underwaterlandscape.com. 250-251 NASA: Image By Norman Kuring, Nasa’s Ocean Color Web. 252 Alamy Stock Photo: Imagebroker (b). 252-253 naturepl. com: Brandon Cole. 254-255 iStockphoto.com: Bitter. 256-257 Science Photo Library: Alexander Semenov. 256 NOAA: Kevin Raskoff, Cal State Monterey / Hidden Ocean Expedition 2005 / NOAA / OAR / OER (ca). 258 Alamy Stock Photo: Science History Images / Eric Grave (tc). Science Photo Library: Wim Van Egmond (tl, cl, cr); Raul Gonzalez (tr); Marek Mis (c). 259 Alamy Stock Photo: Scenics & Science (tr). Jan van IJken Photography & Film: (br). Science Photo Library: Wim Van Egmond (tl, tc, cl); Marek Mis (ftl); M. I. Walker (fcl). 260-261 Science Photo Library: Alexander Semenov. 261 Alamy Stock Photo: Nature Photographers Ltd / Paul R. Sterry (tr). 262 naturepl.com: David Shale (crb, cl). 262-263 naturepl.com: David Fleetham. 263 Nat Geo Image

acknowledgements

Photo: Stephen Frink Collection (br). 162 Dreamstime.com: Isselee (clb); Isselee (bc, crb). 163 Dreamstime. com: Izanbar. 164 Getty Images: DEA / N. Cirani / De Agostini. 165 Alamy Stock Photo: Heritage Image Partnership Ltd / Werner Forman Archive / Art Gallery of New South Wales, Sydney (tl); Heritage Image Partnership Ltd / Werner Forman Archive / Private Collection, Prague (cl). 167 Getty Images: Giordano Cipriani / The Image Bank (crb). 168-169 Dreamstime.com: Isselee. 168 Getty Images: Hal Beral / Corbis (tr). 169 Dreamstime.com: Isselee (b). 170 Alamy Stock Photo: Jane Gould (bl). 174 iStockphoto. com: Marrio31 (cr). Minden Pictures: Becca Saunders (tl). Nat Geo Image Collection: Joel Sartore - National Geographic Photo Ark (tr). naturepl.com: Georgette Douwma (cl); Alex Mustard (tc); Alex Mustard (c); Georgette Douwma (bl); Linda Pitkin (br). 175 Alamy Stock Photo: Reinhard Dirscherl (cl); Andrey Nekrasov (bl). naturepl.com: Fred Bavendam (c); Alex Mustard (tl). 176-177 Alamy Stock Photo: Blue Planet Archive. 176 Getty Images: Michael Aw / Stockbyte (bc). 177 Getty Images: Giordano Cipriani / The Image Bank (tr). 180 Getty Images: DEA / Archivio J. Lange / De Agostini. 181 Alamy Stock Photo: Azoor Travel Photo (tr); The History Collection (cl). 182-183 François Libert | flickr.com/ photos/zsispeo/: (b). 182 Alamy Stock Photo: David Fleetham (t). 183 Alamy Stock Photo: David Fleetham (tr). 184-185 iStockphoto. com: Ilbusca. 186-187 Getty Images: Aukid Phumsirichat / EyeEm. 187 Alamy Stock Photo: NZ Collection (bc). 188-189 Getty Images: Brent Durand / Moment. 189 Alamy Stock Photo: Mauritius Images GmbH (bc). 190 Alamy Stock Photo: The History Collection (tr). 190-191 Nat Geo Image Collection: Cristina Mittermeier. 192 Science Photo Library: Alexander Semenov (c). 193 Ocean Wise Conservation Association: Neil Fisher / Vancouver Aquarium (bc).

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Paul Starosta / Stone. 121 Getty Images: Jay Fleming / Corbis Documentary (crb). 122-123 Dreamstime.com: Jeneses Imre. 124 Science Photo Library: Alexander Semenov. 125 Alamy Stock Photo: Wolfgang Pölzer (crb); World History Archive (cla); Stocktrek Images, Inc. / Brook Peterson (cr). 128-129 Tom Shlesinger. 128 New World Publications Inc: Ned DeLoach (tr). 131 Alamy Stock Photo: Florilegius (cra). 132-133 BioQuest Studios. 132 Science Photo Library: Alexander Semenov (tl). 134 123RF.com: Ten Theeralerttham / Rawangtak (cr). Getty Images: Auscape / Universal Images Group (tc). naturepl.com: Alex Mustard (tr). Alexander Semenov: (c). 135 Alamy Stock Photo: John Anderson (tc). Getty Images: Wild Horizon / Universal Images Group (tr). naturepl.com: Georgette Douwma (cl); Norbert Wu (tl); Jurgen Freund (c); David Shale (cr); Georgette Douwma (fcr). Bo Pardau: (ftr). 136-137 Alamy Stock Photo: Pete Niesen. 136 Getty Images: Oxford Scientific (tc). 138 Science Photo Library: Andrew J. Martinez (tl). 140-141 Yen-Yi Lee, Taiwan. 142-143 BioQuest Studios. 144-145 Maurizio Angelo Pasi. 145 Alamy Stock Photo: Nature Photographers Ltd / Paul R. Sterry (tr). 146-147 Getty Images: BigBlueFun / 500px. 147 Kunstformen der Natur by Ernst Haeckel: (tc). 148 Alamy Stock Photo: Blickwinkel / W. Layer (tl). 148-149 Nat Geo Image Collection: David Doubilet. 150-151 Alamy Stock Photo: David Fleetham. 151 Salty Black Photography by Ernie Black: (tr). 152 Alamy Stock Photo: Agefotostock. 153 123RF.com: Antonio Abrignani (tr). Kunstformen der Natur by Ernst Haeckel. 154 Alamy Stock Photo: Reinhard Dirscherl (tr). 155 Image from the Biodiversity Heritage Library: Atlas Ichthyologique Des Indes Orientales Néêrlandaises : Publié Sous Les Auspices Du Gouvernement Colonial Néêrlandais (tc). 158-159 © Arthur Anker. 158 Alamy Stock

Collection: Emory Kristof (tr). 264-265 Alamy Stock Photo: Nature Picture Library / Alex Mustard. 266 Alamy Stock Photo: Nature Picture Library / Solvin Zankl. 267 Alamy Stock Photo: Chronicle (bc); Nature Picture Library / Solvin Zankl (tr). 268 Dreamstime.com: Aleksey Solodov (tl). Jonathan Lavan | Underpressure Nature Photography: (br). 269 Alamy Stock Photo: Artmedia. 270 Alamy Stock Photo: Jeff Mondragon (bc); Visual&Written Sl / Kelvin Aitken (cr); Andrey Nekrasov (bl). naturepl.com: Gary Bell / Oceanwide (tr); David Shale (tl); Jurgen Freund (cl); Doug Perrine (c). Science Photo Library: Andrew J. Martinez (br). Alexander Semenov: (tc). 271 Science Photo Library: Alexander Semenov (tl, tr, c). Alexander Semenov: (tc). 272-273 Jorge Cervera Hauser / Pelagic Fleet. 273 Getty Images:

Torstenvelden (tc). 274-275 NASA: Goddard Space Flight Center Scientific Visualization Studio. 276-277 Getty Images: Benjamin Lowy / The Image Bank. 278-279 © Jordi Chias Pujol. 279 Alamy Stock Photo: Minden Pictures / Norbert Wu (tr). 280-281 Getty Images: Fine Art / Corbis Historical. 281 Alamy Stock Photo: Art Collection 2 (tr). 282 Alamy Stock Photo: Solvin Zankl (t). 283 Getty Images: E. Widder / HBOI. 284-285 Shawn Heinrichs. 285 Taxidermy by Kevin Halle: (bc). 286 Alamy Stock Photo: David Tipling Photo Library (br). 286-287 Paul Cottis. 288-289 naturepl. com: Doc White. 290-291 NASA: Earth Observatory image created by Robert Simmon, using EO-1 ALI data provided courtesy of the NASA EO-1 team. 292-293 Jorge Cervera Hauser / Pelagic Fleet. 293 naturepl.com: Doug Allan (bc). 294-

295 iStockphoto.com: Zu_09 / Digitalvision Vectors. 296 Alexander Semenov: (tl, tc, bl, bc). 297 Alexander Semenov: (tl, bl). 298-299 Florian Ledoux Photography. 300 Nat Geo Image Collection: Keith Ladzinski (tl). 300-301 naturepl.com: Ingo Arndt. 301 Alamy Stock Photo: National Geographic Image Collection / Paul Nicklen (tr). 302 Alamy Stock Photo: Andrey Nekrasov. 303 Alamy Stock Photo: Paulo Oliveira (tr). 304 naturepl.com: Shane Gross (fcr); Solvin Zankl (cl); Doug Perrine (cr); Solvin Zankl / Geomar (bc); David Shale (br); Solvin Zankl (fbr). 305 Alamy Stock Photo: Nature Picture Library / Doug Perrine (t). naturepl. com: Doug Perrine (c); Solvin Zankl (cl); Solvin Zankl (bl); Solvin Zankl (bc); Solvin Zankl (br). 306-307 Daisy Gilardini Photography. 307 Getty Images: Richard McManus /

Moment (tr). 308 Alamy Stock Photo: Agefotostock / Eric Baccega (b). 309 Valter Bernardeschi. 310-311 Mike Reyfman Photography. 310 naturepl.com: Sylvain Cordier (b). 312-313 © Rasch-Photography | Ralf Schneider. 313 Dreamstime.com: Tarpan (t). 314-315 Alamy Stock Photo: National Geographic Image Collection / Marcin Dobas. 316-317 Getty Images: Sergei Gladyshev / 500px Plus. 317 Alamy Stock Photo: Steve Davey Photography (tr). 318-319 Nat Geo Image Collection: Paul Nicklen. Endpaper Images: Front and Back: Tom Shlesinger All other images © Dorling Kindersley For further information see: www.dkimages.com